diff --git a/completions/Makefile.am b/completions/Makefile.am
index f40943db9d7..d6ec001e358 100644
--- a/completions/Makefile.am
+++ b/completions/Makefile.am
@@ -446,6 +446,7 @@ cross_platform = 2to3 \
 		tcpnice \
 		timeout \
 		tipc \
+		tmux \
 		_tokio-console \
 		tox \
 		tracepath \
diff --git a/completions/tmux b/completions/tmux
new file mode 100644
index 00000000000..b3ccafbd294
--- /dev/null
+++ b/completions/tmux
@@ -0,0 +1,318 @@
+# tmux(1) completion                                       -*- shell-script -*-
+# SPDX-License-Identifier: GPL-2.0-or-later OR ISC
+
+# Log a message to help with debugging.
+# If BASH_COMPLETION_DEBUG is set, it will be printed to stderr.
+# When running with `set -x`, the _comp_cmd_tmux__log call itself will be
+# printed.
+#
+# @param $1 Message to log
+_comp_cmd_tmux__log()
+{
+    if [[ ${BASH_COMPLETION_DEBUG-} ]]; then
+        printf 'tmux bash completion: %s\n' "$1" >&2
+    fi
+}
+
+# Run the tmux command being completed.
+#
+# @param $@ args to tmux
+_comp_cmd_tmux__run()
+{
+    local -a REPLY
+    _comp_dequote "${comp_args[0]-}" || REPLY=("${comp_args[0]-}")
+    LC_ALL=C "${REPLY[0]}" "$@"
+}
+
+# Parse usage output from tmux.
+#
+# @param $1 Usage from tmux, not including the (sub)command name.
+# @var[out] options associative array mapping options to their value types, or
+#     to the empty string if the option doesn't take a value
+# @var[out] args indexed array of positional arg types
+_comp_cmd_tmux__parse_usage()
+{
+    options=()
+    args=()
+
+    local i j
+    local words
+    _comp_split words "$1"
+    for ((i = 0; i < ${#words[@]}; i++)); do
+        case ${words[i]} in
+            "[-"*"]")
+                # One or more options that don't take arguments, either of the
+                # form `[-abc]` or `[-a|-b|-c]`
+                for ((j = 2; j < ${#words[i]} - 1; j++)); do
+                    if [[ ${words[i]:j:1} != [-\|] ]]; then
+                        options+=(["-${words[i]:j:1}"]="")
+                    fi
+                done
+                ;;
+            "[-"*)
+                # One option that does take an argument.
+                if [[ ${words[i + 1]-} != *"]" ]]; then
+                    _comp_cmd_tmux__log \
+                        "Can't parse option: '${words[*]:i:2}' in '$1'"
+                    break
+                fi
+                options+=(["${words[i]#"["}"]="${words[i + 1]%"]"}")
+                ((i++))
+                ;;
+            -*)
+                _comp_cmd_tmux__log "Can't parse option '${words[i]}' in '$1'"
+                break
+                ;;
+            *)
+                # Start of positional arguments.
+                args=("${words[@]:i}")
+                break
+                ;;
+        esac
+    done
+
+    if [[ ${BASH_COMPLETION_DEBUG-} || -o xtrace ]]; then
+        local arg
+        for arg in "${!options[@]}"; do
+            _comp_cmd_tmux__log "option: ${arg} ${options["$arg"]}"
+        done
+        for arg in "${args[@]}"; do
+            _comp_cmd_tmux__log "arg: ${arg}"
+        done
+    fi
+}
+
+# Complete a value either as the argument to an option or as a positional arg.
+#
+# @param $1 subcommand that the value is for, or 'tmux' if it's top-level
+# @param $2 type of the value, from _comp_cmd_tmux__parse_usage()
+_comp_cmd_tmux__value()
+{
+    local subcommand=$1 option_type=$2
+    _comp_cmd_tmux__log \
+        "Trying to complete '$option_type' for subcommand '$subcommand'"
+
+    # To get a list of these argument types, look at `tmux -h` and:
+    #
+    # tmux list-commands -F "#{command_list_usage}" |
+    #   sed 's/[][ ]/\n/g' |
+    #   grep -v ^- |
+    #   sort -u
+    #
+    # TODO: Complete more option types.
+    case $option_type in
+        command)
+            _comp_compgen_split -l -- "$(_comp_cmd_tmux__run \
+                list-commands -F "#{command_list_name}")"
+            ;;
+        directory | *-directory)
+            _comp_compgen_filedir -d
+            ;;
+        file | *-file | path | *-path)
+            _comp_compgen_filedir
+            ;;
+    esac
+}
+
+# Parse command line options to tmux or a subcommand.
+#
+# @param $@ args to tmux or a subcommand, starting with the (sub)command
+#     itself, ending before the current word to complete
+# @var[in] options from _comp_cmd_tmux__parse_usage()
+# @var[out] option_type if the word to complete is the value of an option, this
+#     is the type of that value, otherwise it's empty
+# @var[out] positional_start if option_type is empty, index in $@ of the first
+#     positional argument, or the last index plus 1 if the next word is the
+#     first positional argument, or -1 if the next word could be either the
+#     first positional argument or another option
+_comp_cmd_tmux__options()
+{
+    local command_args=("$@")
+    option_type=""
+    positional_start=-1
+
+    local i
+    for ((i = 1; i < ${#command_args[@]}; i++)); do
+        if [[ $option_type ]]; then
+            # arg to the previous option
+            option_type=""
+        elif [[ ${command_args[i]} == -- ]]; then
+            option_type=""
+            ((positional_start = i + 1))
+            return
+        elif [[ ${command_args[i]} == -?* ]]; then
+            # 1 or more options, possibly also with the value of an option.
+            # E.g., if `-a` and `-b` take no values and `-c` does, `-ab` would
+            # be equivalent to `-a -b` and `-acb` would be `-a` and `-c` with a
+            # value of `b`.
+            local j
+            for ((j = 1; j < ${#command_args[i]}; j++)); do
+                if [[ $option_type ]]; then
+                    # arg has both the option and its value
+                    option_type=""
+                    break
+                fi
+                option_type=${options["-${command_args[i]:j:1}"]-}
+            done
+        else
+            # first positional arg
+            ((positional_start = i))
+            return
+        fi
+    done
+}
+
+# Complete arguments to a subcommand.
+#
+# @param $@ the subcommand followed by its args, ending before the current word
+#     to complete
+_comp_cmd_tmux__subcommand()
+{
+    local subcommand_args=("$@")
+    local usage=$(_comp_cmd_tmux__run list-commands \
+        -F "#{command_list_name} #{command_list_usage}" -- "$1" 2>/dev/null)
+    if [[ ! $usage ]]; then
+        _comp_cmd_tmux__log "Unknown tmux subcommand: '$1'"
+        return
+    fi
+    local subcommand=${usage%% *} # not $1, because it could be an alias
+    _comp_cmd_tmux__log "Attempting completion for 'tmux $subcommand'"
+
+    local -A options
+    local -a args
+    _comp_cmd_tmux__parse_usage "${usage#* }"
+
+    local option_type
+    local positional_start
+    _comp_cmd_tmux__options "${subcommand_args[@]}"
+
+    if [[ $option_type ]]; then
+        _comp_cmd_tmux__value "$subcommand" "$option_type"
+        return
+    elif ((positional_start < 0)) && [[ $cur == -* ]]; then
+        _comp_compgen -- -W '"${!options[@]}"'
+        return
+    elif ((positional_start < 0)); then
+        # $cur (one past the end of subcommand_args) is the first positional
+        # arg
+        positional_start=${#subcommand_args[@]}
+    fi
+
+    if [[ $subcommand == display-menu ]]; then
+        # display-menu has a non-trivial repeating pattern of positional args
+        # that would need custom logic to support correctly, and it's probably
+        # used in config files or shell scripts more than interactively anyway.
+        _comp_cmd_tmux__log \
+            "Not completing positional args for 'tmux $subcommand'"
+        return
+    fi
+
+    _comp_cmd_tmux__log \
+        "'tmux $subcommand' first positional arg: '${subcommand_args[positional_start]-}'"
+
+    local args_index=$positional_start
+    local usage_args_index
+    local prev_arg_type=""
+    for ((\
+    usage_args_index = 0;  \
+    usage_args_index < ${#args[@]};  \
+    args_index++, usage_args_index++)); do
+        local arg_type=${args[usage_args_index]##+(\[)}
+        arg_type=${arg_type%%+(\])}
+        if [[ $arg_type == ... ]]; then
+            if ((usage_args_index == 0)); then
+                _comp_cmd_tmux__log "'tmux $subcommand' first arg is '...'"
+                return
+            elif ((usage_args_index != ${#args[@]} - 1)); then
+                _comp_cmd_tmux__log \
+                    "'tmux $subcommand' usage has '...' before last arg"
+                return
+            fi
+            # https://man.openbsd.org/style says "Usage statements should take
+            # the same form as the synopsis in manual pages."
+            # https://mandoc.bsd.lv/mdoc/intro/synopsis_util.html says "Some
+            # commands can optionally take more than one argument of the same
+            # kind. This is indicated by an ellipsis trailing the respective Ar
+            # macro." tmux seems to mostly use `...` in that way to only repeat
+            # the previous argument. In display-menu it uses `...` to repeat
+            # all arguments instead, but that subcommand is explicitly ignored
+            # above.
+            _comp_cmd_tmux__value "$subcommand" "$prev_arg_type"
+            return
+        elif [[ $arg_type == arguments ]]; then
+            if [[ $prev_arg_type == command ]] &&
+                ((usage_args_index == ${#args[@]} - 1)); then
+                # The usage ends in `command arguments`, so recurse to the new
+                # subcommand.
+                _comp_cmd_tmux__subcommand \
+                    "${subcommand_args[@]:args_index-1}"
+                return
+            else
+                _comp_cmd_tmux__log \
+                    "'tmux $subcommand' has unsupported 'arguments' in usage"
+                return
+            fi
+        elif ((args_index == ${#subcommand_args[@]})); then
+            # The usage arg is 1 past the end of $subcommand_args, so complete
+            # it.
+            _comp_cmd_tmux__value "$subcommand" "$arg_type"
+            return
+        fi
+        prev_arg_type=$arg_type
+    done
+
+    _comp_cmd_tmux__log "Too many args to 'tmux $subcommand'"
+}
+
+_comp_cmd_tmux()
+{
+    local cur prev words cword comp_args
+    _comp_initialize -- "$@" || return
+
+    local usage
+    usage=$(_comp_cmd_tmux__run -h 2>&1)
+    # Before https://github.com/tmux/tmux/pull/4455 (merged 2025-04-09), `-h`
+    # produced usage information because it was an error, so we have to trim
+    # the error message too.
+    usage=${usage#$'tmux: unknown option -- h\n'}
+    usage=${usage#usage: tmux }
+
+    local -A options
+    local -a args
+    _comp_cmd_tmux__parse_usage "$usage"
+
+    local option_type
+    local positional_start
+    _comp_cmd_tmux__options "${words[@]:0:cword}"
+
+    if [[ $option_type ]]; then
+        _comp_cmd_tmux__value tmux "$option_type"
+        return
+    elif ((positional_start < 0)) && [[ $cur == -* ]]; then
+        _comp_compgen -- -W '"${!options[@]}"'
+        return
+    elif ((positional_start < 0)); then
+        ((positional_start = cword))
+    fi
+
+    local i
+    local -a REPLY
+    local subcommand_start=$positional_start
+    for ((i = positional_start; i < cword; i++)); do
+        if _comp_dequote "${words[i]}" && [[ ${REPLY[-1]-} =~ (\\*)\;$ ]] &&
+            ((${#BASH_REMATCH[1]} % 2 == 0)); then
+            # end of current command
+            ((subcommand_start = i + 1))
+        fi
+    done
+
+    if ((cword == subcommand_start)); then
+        _comp_cmd_tmux__value tmux command
+    else
+        _comp_cmd_tmux__subcommand \
+            "${words[@]:subcommand_start:cword-subcommand_start}"
+    fi
+} &&
+    complete -F _comp_cmd_tmux tmux
+
+# ex: filetype=sh
diff --git a/test/t/Makefile.am b/test/t/Makefile.am
index 8b70c935cee..7ed95e424fa 100644
--- a/test/t/Makefile.am
+++ b/test/t/Makefile.am
@@ -624,6 +624,7 @@ EXTRA_DIST = \
 	test_time.py \
 	test_timeout.py \
 	test_tipc.py \
+	test_tmux.py \
 	test_totem.py \
 	test_touch.py \
 	test_tox.py \
diff --git a/test/t/test_tmux.py b/test/t/test_tmux.py
new file mode 100644
index 00000000000..73ee0a54a9b
--- /dev/null
+++ b/test/t/test_tmux.py
@@ -0,0 +1,169 @@
+# SPDX-License-Identifier: GPL-2.0-or-later OR ISC
+
+import pytest
+
+from conftest import assert_complete
+
+
+@pytest.mark.bashcomp(cmd="tmux", require_cmd=True)
+class TestTmux:
+    # Tests for _comp_cmd_tmux__parse_usage(). Most of this function is tested
+    # elsewhere since almost everything else depends on it. These are just
+    # tests for corner cases that aren't tested elsewhere.
+
+    @pytest.mark.complete("tmux wait-for -")
+    def test_parse_usage_alternative_options(self, completion):
+        """Tests the [-a|-b|-c] form of option parsing."""
+        assert "-L" in completion
+        assert "-S" in completion
+        assert "-U" in completion
+        assert "-|" not in completion
+        assert "--" not in completion
+
+    # Tests for _comp_cmd_tmux__value()
+
+    @pytest.mark.complete("tmux new-")
+    def test_value_command(self, completion):
+        assert "new-session" in completion
+        assert "new-window" in completion
+
+    @pytest.mark.complete("tmux new-window -c ", cwd="shared/default")
+    def test_value_directory(self, completion):
+        assert completion == ["bar bar.d/", "foo.d/"]
+
+    @pytest.mark.complete("tmux -f ", cwd="shared/default")
+    def test_value_file(self, completion):
+        assert completion == ["bar", "bar bar.d/", "foo", "foo.d/"]
+
+    # Tests for _comp_cmd_tmux__options()
+
+    @pytest.mark.complete("tmux -f /dev/null ")
+    def test_option_with_value(self, completion):
+        assert "new-session" in completion
+
+    @pytest.mark.complete("tmux -Nvf /dev/null ")
+    def test_option_multiple_with_value(self, completion):
+        assert "new-session" in completion
+
+    @pytest.mark.complete("tmux -f -f ")
+    def test_option_with_value_with_dash(self, completion):
+        """Tests that the second -f is a filename not an option."""
+        assert "new-session" in completion
+
+    @pytest.mark.complete("tmux -- ")
+    def test_option_explicit_end(self, completion):
+        assert "new-session" in completion
+
+    @pytest.mark.complete("tmux -f/dev/null ")
+    def test_option_with_attached_value(self, completion):
+        assert "new-session" in completion
+
+    @pytest.mark.complete("tmux -Nvf/dev/null ")
+    def test_option_multiple_with_attached_value(self, completion):
+        assert "new-session" in completion
+
+    @pytest.mark.complete("tmux -v ")
+    def test_option_without_value(self, completion):
+        assert "new-session" in completion
+
+    @pytest.mark.complete("tmux -Nv ")
+    def test_option_multiple_without_value(self, completion):
+        assert "new-session" in completion
+
+    # Tests for _comp_cmd_tmux__subcommand()
+
+    @pytest.mark.complete("tmux this-is-not-a-real-subcommand-i-hope ")
+    def test_subcommand_unknown(self, completion):
+        assert not completion
+
+    @pytest.mark.complete("tmux new-window -c ", cwd="shared/default")
+    def test_subcommand_option_value(self, completion):
+        assert completion == ["bar bar.d/", "foo.d/"]
+
+    @pytest.mark.complete("tmux new-window -")
+    def test_subcommand_options(self, completion):
+        assert "-a" in completion  # takes no value
+        assert "-c" in completion  # takes a value
+
+    @pytest.mark.complete("tmux display-menu ")
+    def test_subcommand_no_positional_arg_completion(self, completion):
+        assert not completion
+
+    @pytest.mark.complete("tmux source-file abc def ", cwd="shared/default")
+    def test_subcommand_repetition(self, completion):
+        assert completion == ["bar", "bar bar.d/", "foo", "foo.d/"]
+
+    @pytest.mark.complete(
+        "tmux bind-key C-a new-window -c ",
+        cwd="shared/default",
+    )
+    def test_subcommand_recursion(self, completion):
+        assert completion == ["bar bar.d/", "foo.d/"]
+
+    @pytest.mark.complete("tmux source-file ", cwd="shared/default")
+    def test_subcommand_positional_arg_1(self, completion):
+        assert completion == ["bar", "bar bar.d/", "foo", "foo.d/"]
+
+    @pytest.mark.complete("tmux bind-key C-a ")
+    def test_subcommand_positional_arg_2(self, completion):
+        assert "new-session" in completion
+
+    @pytest.mark.complete("tmux start-server ")
+    def test_subcommand_no_positional_args(self, completion):
+        assert not completion
+
+    @pytest.mark.complete("tmux choose-tree abc def ghi ")
+    def test_subcommand_too_many_positional_args(self, completion):
+        assert not completion
+
+    # Tests for _comp_cmd_tmux()
+
+    @pytest.mark.complete("tmux -f ", cwd="shared/default")
+    def test_tmux_option_value(self, completion):
+        assert completion == ["bar", "bar bar.d/", "foo", "foo.d/"]
+
+    @pytest.mark.complete("tmux -")
+    def test_tmux_options(self, completion):
+        assert "-f" in completion  # takes a value
+        assert "-v" in completion  # takes no value
+
+    @pytest.mark.parametrize(
+        "other_commands",
+        [
+            r"foo ';'",
+            r"foo';'",
+            r"foo '\\;'",  # backslash escaped in tmux
+            r"foo'\\;'",
+        ],
+    )
+    def test_tmux_multiple_commands(self, bash, other_commands):
+        completion = assert_complete(
+            bash,
+            f"tmux {other_commands} bind-key C-a ",
+        )
+        assert "new-session" in completion
+
+    @pytest.mark.parametrize(
+        "semicolon_arg",
+        [
+            r"foo '\;'",  # semicolon escaped in tmux
+            r"foo'\;'",
+            r"foo '\\\;'",  # escaped backslash then escaped semicolon in tmux
+            r"foo'\\\;'",
+            r"foo';'bar",  # semicolon doesn't need to be escaped in the middle
+        ],
+    )
+    def test_tmux_semicolon_within_subcommand(self, bash, semicolon_arg):
+        completion = assert_complete(
+            bash,
+            # Note that the next arg is a file, not a subcommand. If it were a
+            # subcommand, it wouldn't be possible to tell if the completion was
+            # parsing semicolon_arg correctly.
+            f"tmux source-file {semicolon_arg} ",
+            cwd="shared/default",
+        )
+        assert completion == ["bar", "bar bar.d/", "foo", "foo.d/"]
+
+    @pytest.mark.complete("tmux ")
+    def test_tmux_subcommand(self, completion):
+        assert "new-session" in completion