diff --git a/CHANGELOG.next.asciidoc b/CHANGELOG.next.asciidoc
index d189637976d..490e17153fc 100644
--- a/CHANGELOG.next.asciidoc
+++ b/CHANGELOG.next.asciidoc
@@ -315,6 +315,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Improve ECS categorization field mappings in system module. {issue}16031[16031] {pull}18065[18065]
 - Change the `json.*` input settings implementation to merge parsed json objects with existing objects in the event instead of fully replacing them. {pull}17958[17958]
 - Improve ECS categorization field mappings in osquery module. {issue}16176[16176] {pull}17881[17881]
+- The `logstash` module can now automatically detect the log file format (JSON or plaintext) and process it accordingly. {issue}9964[9964] {pull}18095[18095]
 
 *Heartbeat*
 
diff --git a/filebeat/docs/modules/logstash.asciidoc b/filebeat/docs/modules/logstash.asciidoc
index 2a9ace71d1b..5c9df956e05 100644
--- a/filebeat/docs/modules/logstash.asciidoc
+++ b/filebeat/docs/modules/logstash.asciidoc
@@ -8,8 +8,8 @@ This file is generated! See scripts/docs_collector.py
 
 == Logstash module
 
-The +{modulename}+ module parse logstash regular logs and the slow log, it will support the plain text format
-and the JSON format (--log.format json). The default is the plain text format.
+The +{modulename}+ modules parse logstash regular logs and the slow log, it will support the plain text format
+and the JSON format.
 
 include::../include/what-happens.asciidoc[]
 
@@ -34,7 +34,7 @@ The Logstash `slowlog` fileset was tested with logs from Logstash 5.6 and 6.0
 include::../include/configuring-intro.asciidoc[]
 
 The following example shows how to set paths in the +modules.d/{modulename}.yml+
-file to override the default paths for Logstash logs and set the format to json
+file to override the default paths for Logstash logs.
 
 ["source","yaml",subs="attributes"]
 -----
@@ -42,11 +42,9 @@ file to override the default paths for Logstash logs and set the format to json
   log:
     enabled: true
     var.paths: ["/path/to/log/logstash.log*"]
-    var.format: json
   slowlog:
     enabled: true
     var.paths: ["/path/to/log/logstash-slowlog.log*"]
-    var.format: json
 -----
 
 To specify the same settings at the command line, you use:
@@ -68,21 +66,11 @@ include::../include/config-option-intro.asciidoc[]
 
 include::../include/var-paths.asciidoc[]
 
-*`var.format`*::
-
-The configured Logstash log format. Possible values are: `json` or `plain`. The
-default is `plain`.
-
 [float]
 ==== `slowlog` fileset settings
 
 include::../include/var-paths.asciidoc[]
 
-*`var.format`*::
-
-The configured Logstash log format. Possible values are: `json` or `plain`. The
-default is `plain`.
-
 include::../include/timezone-support.asciidoc[]
 
 [float]
@@ -96,6 +84,11 @@ image::./images/kibana-logstash-log.png[]
 [role="screenshot"]
 image::./images/kibana-logstash-slowlog.png[]
 
+[float]
+=== Known issues
+When using the `log` fileset to parse plaintext logs, if a multiline plaintext log contains an embedded JSON objct such that
+the JSON object starts on a new line, the fileset may not parse the multiline plaintext log event correctly.
+
 :has-dashboards!:
 
 :fileset_ex!:
diff --git a/filebeat/module/logstash/_meta/docs.asciidoc b/filebeat/module/logstash/_meta/docs.asciidoc
index 2fc59161812..8f4e0d33a3c 100644
--- a/filebeat/module/logstash/_meta/docs.asciidoc
+++ b/filebeat/module/logstash/_meta/docs.asciidoc
@@ -3,8 +3,8 @@
 
 == Logstash module
 
-The +{modulename}+ module parse logstash regular logs and the slow log, it will support the plain text format
-and the JSON format (--log.format json). The default is the plain text format.
+The +{modulename}+ modules parse logstash regular logs and the slow log, it will support the plain text format
+and the JSON format.
 
 include::../include/what-happens.asciidoc[]
 
@@ -29,7 +29,7 @@ The Logstash `slowlog` fileset was tested with logs from Logstash 5.6 and 6.0
 include::../include/configuring-intro.asciidoc[]
 
 The following example shows how to set paths in the +modules.d/{modulename}.yml+
-file to override the default paths for Logstash logs and set the format to json
+file to override the default paths for Logstash logs.
 
 ["source","yaml",subs="attributes"]
 -----
@@ -37,11 +37,9 @@ file to override the default paths for Logstash logs and set the format to json
   log:
     enabled: true
     var.paths: ["/path/to/log/logstash.log*"]
-    var.format: json
   slowlog:
     enabled: true
     var.paths: ["/path/to/log/logstash-slowlog.log*"]
-    var.format: json
 -----
 
 To specify the same settings at the command line, you use:
@@ -63,21 +61,11 @@ include::../include/config-option-intro.asciidoc[]
 
 include::../include/var-paths.asciidoc[]
 
-*`var.format`*::
-
-The configured Logstash log format. Possible values are: `json` or `plain`. The
-default is `plain`.
-
 [float]
 ==== `slowlog` fileset settings
 
 include::../include/var-paths.asciidoc[]
 
-*`var.format`*::
-
-The configured Logstash log format. Possible values are: `json` or `plain`. The
-default is `plain`.
-
 include::../include/timezone-support.asciidoc[]
 
 [float]
@@ -91,6 +79,11 @@ image::./images/kibana-logstash-log.png[]
 [role="screenshot"]
 image::./images/kibana-logstash-slowlog.png[]
 
+[float]
+=== Known issues
+When using the `log` fileset to parse plaintext logs, if a multiline plaintext log contains an embedded JSON objct such that
+the JSON object starts on a new line, the fileset may not parse the multiline plaintext log event correctly.
+
 :has-dashboards!:
 
 :fileset_ex!:
diff --git a/filebeat/module/logstash/log/config/log.yml b/filebeat/module/logstash/log/config/log.yml
index 27140697f77..af0e4c33735 100644
--- a/filebeat/module/logstash/log/config/log.yml
+++ b/filebeat/module/logstash/log/config/log.yml
@@ -5,12 +5,10 @@ paths:
 {{ end }}
 exclude_files: [".gz$"]
 
-{{ if eq .format "plain" }}
 multiline:
-  pattern: ^\[[0-9]{4}-[0-9]{2}-[0-9]{2}
+  pattern: ^((\[[0-9]{4}-[0-9]{2}-[0-9]{2}[^\]]+\])|({.+}))
   negate: true
   match: after
-{{ end }}
 
 processors:
 # Locale for time zone is only needed in non-json logs
diff --git a/filebeat/module/logstash/log/ingest/pipeline-json.yml b/filebeat/module/logstash/log/ingest/pipeline-json.yml
index 28d6c6f95eb..f14a3be2855 100644
--- a/filebeat/module/logstash/log/ingest/pipeline-json.yml
+++ b/filebeat/module/logstash/log/ingest/pipeline-json.yml
@@ -7,9 +7,6 @@ processors:
 - json:
     field: message
     target_field: logstash.log
-- rename:
-    field: '@timestamp'
-    target_field: event.created
 - convert:
     field: logstash.log.timeMillis
     type: string
diff --git a/filebeat/module/logstash/log/ingest/pipeline-plain.yml b/filebeat/module/logstash/log/ingest/pipeline-plaintext.yml
similarity index 96%
rename from filebeat/module/logstash/log/ingest/pipeline-plain.yml
rename to filebeat/module/logstash/log/ingest/pipeline-plaintext.yml
index 6ec17b74073..4c75de47c99 100644
--- a/filebeat/module/logstash/log/ingest/pipeline-plain.yml
+++ b/filebeat/module/logstash/log/ingest/pipeline-plaintext.yml
@@ -17,9 +17,6 @@ processors:
       %{GREEDYMULTILINE:message}
     - \[%{TIMESTAMP_ISO8601:logstash.log.timestamp}\]\[%{LOGSTASH_LOGLEVEL:log.level}\s?\]\[%{LOGSTASH_CLASS_MODULE:logstash.log.module}\s*\]
       %{GREEDYMULTILINE:message}
-- rename:
-    field: '@timestamp'
-    target_field: event.created
 - date:
     if: ctx.event.timezone == null
     field: logstash.log.timestamp
diff --git a/filebeat/module/logstash/log/ingest/pipeline.yml b/filebeat/module/logstash/log/ingest/pipeline.yml
new file mode 100644
index 00000000000..0a416e5758e
--- /dev/null
+++ b/filebeat/module/logstash/log/ingest/pipeline.yml
@@ -0,0 +1,24 @@
+description: Pipeline for parsing logstash node logs
+processors:
+- rename:
+    field: '@timestamp'
+    target_field: event.created
+- grok:
+    field: message
+    patterns:
+      - ^%{CHAR:first_char}
+    pattern_definitions:
+      CHAR: .
+- pipeline:
+    if: ctx.first_char != '{'
+    name: '{< IngestPipeline "pipeline-plaintext" >}'
+- pipeline:
+    if: ctx.first_char == '{'
+    name: '{< IngestPipeline "pipeline-json" >}'
+- remove:
+    field:
+      - first_char
+on_failure:
+  - set:
+      field: error.message
+      value: '{{ _ingest.on_failure_message }}'
diff --git a/filebeat/module/logstash/log/manifest.yml b/filebeat/module/logstash/log/manifest.yml
index b5ea4edafe1..c1c231ca5f3 100644
--- a/filebeat/module/logstash/log/manifest.yml
+++ b/filebeat/module/logstash/log/manifest.yml
@@ -1,13 +1,16 @@
 module_version: 1.0
 
 var:
-  - name: format
-    default: plain
   - name: paths
     default:
-      - /var/log/logstash/logstash-{{.format}}*.log
+      - /var/log/logstash/logstash-plain*.log
+      - /var/log/logstash/logstash-json*.log
     os.windows:
-      - c:/programdata/logstash/logs/logstash-{{.format}}*.log
+      - c:/programdata/logstash/logs/logstash-plain*.log
+      - c:/programdata/logstash/logs/logstash-json*.log
 
-ingest_pipeline: ingest/pipeline-{{.format}}.yml
+ingest_pipeline:
+  - ingest/pipeline.yml
+  - ingest/pipeline-plaintext.yml
+  - ingest/pipeline-json.yml
 input: config/log.yml
diff --git a/filebeat/module/logstash/log/test/logstash-plain-7.4.log-expected.json b/filebeat/module/logstash/log/test/logstash-plain-7.4.log-expected.json
index b9b93ff3140..c37f8d70590 100644
--- a/filebeat/module/logstash/log/test/logstash-plain-7.4.log-expected.json
+++ b/filebeat/module/logstash/log/test/logstash-plain-7.4.log-expected.json
@@ -31,4 +31,4 @@
         "message": "Encountered a retryable error. Will Retry with exponential backoff...",
         "service.type": "logstash"
     }
-]
+]
\ No newline at end of file
diff --git a/filebeat/module/logstash/log/test/logstash-plain.log b/filebeat/module/logstash/log/test/logstash-plain.log
index d65e2af70bb..6e270e00d85 100644
--- a/filebeat/module/logstash/log/test/logstash-plain.log
+++ b/filebeat/module/logstash/log/test/logstash-plain.log
@@ -2,4 +2,10 @@
 [2017-11-20T03:55:00,318][INFO ][logstash.inputs.jdbc     ] (0.058950s) Select Name as [person.name]
 , Address as [person.address]
 from people
-
+[2020-05-13T11:00:26,431][INFO ][logstash.inputs.json     ] (0.158950s) {
+"foo": [
+{
+  "bar": "baz"
+}
+]
+}
diff --git a/filebeat/module/logstash/log/test/logstash-plain.log-expected.json b/filebeat/module/logstash/log/test/logstash-plain.log-expected.json
index 983fd1ef14c..a39376e1ec4 100644
--- a/filebeat/module/logstash/log/test/logstash-plain.log-expected.json
+++ b/filebeat/module/logstash/log/test/logstash-plain.log-expected.json
@@ -29,7 +29,25 @@
         "log.level": "INFO",
         "log.offset": 175,
         "logstash.log.module": "logstash.inputs.jdbc",
-        "message": "(0.058950s) Select Name as [person.name]\n, Address as [person.address]\nfrom people\n",
+        "message": "(0.058950s) Select Name as [person.name]\n, Address as [person.address]\nfrom people",
+        "service.type": "logstash"
+    },
+    {
+        "@timestamp": "2020-05-13T11:00:26.431-02:00",
+        "event.dataset": "logstash.log",
+        "event.kind": "event",
+        "event.module": "logstash",
+        "event.timezone": "-02:00",
+        "event.type": "info",
+        "fileset.name": "log",
+        "input.type": "log",
+        "log.flags": [
+            "multiline"
+        ],
+        "log.level": "INFO",
+        "log.offset": 318,
+        "logstash.log.module": "logstash.inputs.json",
+        "message": "(0.158950s) {\n\"foo\": [\n{\n  \"bar\": \"baz\"\n}\n]\n}",
         "service.type": "logstash"
     }
 ]
\ No newline at end of file
diff --git a/filebeat/module/logstash/slowlog/ingest/pipeline-json.yml b/filebeat/module/logstash/slowlog/ingest/pipeline-json.yml
index acfd95a08d2..d68b3eb9eee 100644
--- a/filebeat/module/logstash/slowlog/ingest/pipeline-json.yml
+++ b/filebeat/module/logstash/slowlog/ingest/pipeline-json.yml
@@ -7,9 +7,6 @@ processors:
 - json:
     field: message
     target_field: logstash.slowlog
-- rename:
-    field: '@timestamp'
-    target_field: event.created
 - convert:
     field: logstash.slowlog.timeMillis
     type: string
diff --git a/filebeat/module/logstash/slowlog/ingest/pipeline-plain.yml b/filebeat/module/logstash/slowlog/ingest/pipeline-plaintext.yml
similarity index 96%
rename from filebeat/module/logstash/slowlog/ingest/pipeline-plain.yml
rename to filebeat/module/logstash/slowlog/ingest/pipeline-plaintext.yml
index a049b26d603..2ac47879cea 100644
--- a/filebeat/module/logstash/slowlog/ingest/pipeline-plain.yml
+++ b/filebeat/module/logstash/slowlog/ingest/pipeline-plaintext.yml
@@ -21,9 +21,6 @@ processors:
     patterns:
     - '{:plugin_params=>%{GREEDYDATA:logstash.slowlog.plugin_params}, :took_in_nanos=>%{NUMBER:event.duration},
       :took_in_millis=>%{NUMBER:logstash.slowlog.took_in_millis}, :event=>%{GREEDYDATA:logstash.slowlog.event}}'
-- rename:
-    field: '@timestamp'
-    target_field: event.created
 - date:
     if: ctx.event.timezone == null
     field: logstash.slowlog.timestamp
diff --git a/filebeat/module/logstash/slowlog/ingest/pipeline.yml b/filebeat/module/logstash/slowlog/ingest/pipeline.yml
new file mode 100644
index 00000000000..061a4f8c636
--- /dev/null
+++ b/filebeat/module/logstash/slowlog/ingest/pipeline.yml
@@ -0,0 +1,24 @@
+description: Pipeline for parsing logstash slow logs
+processors:
+- rename:
+    field: '@timestamp'
+    target_field: event.created
+- grok:
+    field: message
+    patterns:
+      - ^%{CHAR:first_char}
+    pattern_definitions:
+      CHAR: .
+- pipeline:
+    if: ctx.first_char != '{'
+    name: '{< IngestPipeline "pipeline-plaintext" >}'
+- pipeline:
+    if: ctx.first_char == '{'
+    name: '{< IngestPipeline "pipeline-json" >}'
+- remove:
+    field:
+      - first_char
+on_failure:
+  - set:
+      field: error.message
+      value: '{{ _ingest.on_failure_message }}'
diff --git a/filebeat/module/logstash/slowlog/manifest.yml b/filebeat/module/logstash/slowlog/manifest.yml
index afce6486404..d37f2ebf28c 100644
--- a/filebeat/module/logstash/slowlog/manifest.yml
+++ b/filebeat/module/logstash/slowlog/manifest.yml
@@ -1,13 +1,16 @@
 module_version: 1.0
 
 var:
-  - name: format
-    default: plain
   - name: paths
     default:
-      - /var/log/logstash/logstash-slowlog-{{.format}}*.log
+      - /var/log/logstash/logstash-slowlog-plain*.log
+      - /var/log/logstash/logstash-slowlog-json*.log
     os.windows:
-      - c:/programdata/logstash/logs/logstash-slowlog-{{.format}}*.log
+      - c:/programdata/logstash/logs/logstash-slowlog-plain*.log
+      - c:/programdata/logstash/logs/logstash-slowlog-json*.log
 
-ingest_pipeline: ingest/pipeline-{{.format}}.yml
+ingest_pipeline:
+  - ingest/pipeline.yml
+  - ingest/pipeline-plaintext.yml
+  - ingest/pipeline-json.yml
 input: config/slowlog.yml