diff --git a/pkg/workflow/agentic_engine.go b/pkg/workflow/agentic_engine.go
index 68929de272..afb77705c7 100644
--- a/pkg/workflow/agentic_engine.go
+++ b/pkg/workflow/agentic_engine.go
@@ -279,6 +279,24 @@ func (e *BaseEngine) GetRequiredSecretNames(workflowData *WorkflowData) []string
 	return []string{}
 }
 
+// ParseLogMetrics provides a default no-op implementation for log parsing
+// Engines can override this to provide detailed log parsing and metrics extraction
+func (e *BaseEngine) ParseLogMetrics(logContent string, verbose bool) LogMetrics {
+	return LogMetrics{}
+}
+
+// GetLogParserScriptId returns empty string by default (no JavaScript parser)
+// Engines can override this to provide a JavaScript parser for log analysis
+func (e *BaseEngine) GetLogParserScriptId() string {
+	return ""
+}
+
+// RenderMCPConfig provides a default no-op implementation for MCP configuration
+// Engines can override this to provide custom MCP server configuration
+func (e *BaseEngine) RenderMCPConfig(yaml *strings.Builder, tools map[string]any, mcpTools []string, workflowData *WorkflowData) {
+	// Default implementation does nothing - engines that support MCP should override this
+}
+
 // convertStepToYAML converts a step map to YAML string - uses proper YAML serialization
 // This is a shared implementation inherited by all engines that embed BaseEngine
 func (e *BaseEngine) convertStepToYAML(stepMap map[string]any) (string, error) {
@@ -307,6 +325,7 @@ func NewEngineRegistry() *EngineRegistry {
 	registry.Register(NewClaudeEngine())
 	registry.Register(NewCodexEngine())
 	registry.Register(NewCopilotEngine())
+	registry.Register(NewCustomEngine())
 
 	agenticEngineLog.Printf("Registered %d engines", len(registry.engines))
 	return registry
diff --git a/pkg/workflow/custom_engine.go b/pkg/workflow/custom_engine.go
new file mode 100644
index 0000000000..812a410ddd
--- /dev/null
+++ b/pkg/workflow/custom_engine.go
@@ -0,0 +1,154 @@
+// This file implements the Custom agentic engine.
+//
+// The Custom engine allows users to bring their own AI provider by defining
+// custom installation and execution steps through the engine configuration.
+// This engine provides maximum flexibility for integrating third-party AI tools
+// or custom implementations that aren't natively supported.
+//
+// Configuration Example:
+//
+//	engine:
+//	  id: custom
+//	  command: /path/to/custom/agent  # Optional: Skip installation if command is provided
+//	  steps:                          # Custom installation/setup steps
+//	    - name: Install Custom Agent
+//	      run: |
+//	        curl -sSL https://example.com/install.sh | bash
+//	  env:                            # Custom environment variables
+//	    CUSTOM_API_KEY: ${{ secrets.CUSTOM_API_KEY }}
+//	  args:                           # Custom command-line arguments
+//	    - --model
+//	    - gpt-4
+
+package workflow
+
+import (
+	"strings"
+
+	"github.com/github/gh-aw/pkg/logger"
+)
+
+var customLog = logger.New("workflow:custom_engine")
+
+// CustomEngine represents a custom agentic engine that allows users to
+// bring their own AI provider with full control over installation and execution.
+type CustomEngine struct {
+	BaseEngine
+}
+
+func NewCustomEngine() *CustomEngine {
+	customLog.Print("Creating new Custom engine instance")
+	return &CustomEngine{
+		BaseEngine: BaseEngine{
+			id:                     "custom",
+			displayName:            "Custom Engine",
+			description:            "Bring your own AI provider with custom installation and execution steps",
+			experimental:           false,
+			supportsToolsAllowlist: false, // Custom engines don't have built-in tool support
+			supportsMaxTurns:       false, // Custom engines must implement max-turns themselves
+			supportsWebFetch:       false, // Custom engines must implement web-fetch themselves
+			supportsWebSearch:      false, // Custom engines must implement web-search themselves
+			supportsFirewall:       false, // Custom engines can implement firewall support if needed
+			supportsPlugins:        false, // Custom engines must implement plugin support themselves
+			supportsLLMGateway:     false, // Custom engines don't have LLM gateway support by default
+		},
+	}
+}
+
+// SupportsLLMGateway returns -1 indicating no LLM gateway support
+func (e *CustomEngine) SupportsLLMGateway() int {
+	return -1
+}
+
+// GetRequiredSecretNames returns an empty list since custom engines define their own secrets
+// Users should declare required secrets through the engine.env configuration
+func (e *CustomEngine) GetRequiredSecretNames(workflowData *WorkflowData) []string {
+	customLog.Print("Custom engine does not require predefined secrets")
+	return []string{}
+}
+
+// GetInstallationSteps returns custom installation steps defined in engine configuration
+// If engine.command is specified, installation steps are skipped
+func (e *CustomEngine) GetInstallationSteps(workflowData *WorkflowData) []GitHubActionStep {
+	customLog.Print("Generating installation steps for custom engine")
+
+	// If command is specified, skip installation (user provides their own executable)
+	if workflowData.EngineConfig != nil && workflowData.EngineConfig.Command != "" {
+		customLog.Printf("Skipping installation - custom command specified: %s", workflowData.EngineConfig.Command)
+		return []GitHubActionStep{}
+	}
+
+	// Return custom steps from engine configuration using the shared helper
+	steps := InjectCustomEngineSteps(workflowData, e.convertStepToYAML)
+
+	customLog.Printf("Generated %d installation steps from engine configuration", len(steps))
+	return steps
+}
+
+// GetExecutionSteps returns execution steps for the custom engine
+// This is typically defined by users through the engine configuration
+func (e *CustomEngine) GetExecutionSteps(workflowData *WorkflowData, logFile string) []GitHubActionStep {
+	customLog.Print("Generating execution steps for custom engine")
+
+	steps := []GitHubActionStep{}
+
+	// Custom engines must provide their own execution logic through:
+	// 1. engine.command - path to the executable
+	// 2. engine.args - command-line arguments
+	// 3. Custom environment variables via engine.env
+	//
+	// Users are responsible for:
+	// - Installing their AI provider (via engine.steps)
+	// - Configuring authentication (via engine.env with secrets)
+	// - Executing the agent with the prompt
+	// - Handling tool integration if needed
+
+	if workflowData.EngineConfig != nil {
+		if workflowData.EngineConfig.Command != "" {
+			customLog.Printf("Custom command specified: %s", workflowData.EngineConfig.Command)
+		}
+		if len(workflowData.EngineConfig.Args) > 0 {
+			customLog.Printf("Custom args: %v", workflowData.EngineConfig.Args)
+		}
+		if len(workflowData.EngineConfig.Env) > 0 {
+			customLog.Printf("Custom env vars: %d", len(workflowData.EngineConfig.Env))
+		}
+	}
+
+	// Custom engines should document their execution pattern in comments
+	steps = append(steps, GitHubActionStep{
+		"      # Custom Engine Execution",
+		"      # This engine expects users to define their own execution steps through:",
+		"      #   - engine.command: Path to the AI agent executable",
+		"      #   - engine.args: Command-line arguments to pass to the agent",
+		"      #   - engine.env: Environment variables for authentication and configuration",
+		"      #",
+		"      # Example configuration:",
+		"      # engine:",
+		"      #   id: custom",
+		"      #   command: /usr/local/bin/my-agent",
+		"      #   args: [\"--model\", \"gpt-4\", \"--prompt\", \"$PROMPT\"]",
+		"      #   env:",
+		"      #     API_KEY: ${{ secrets.MY_API_KEY }}",
+	})
+
+	customLog.Printf("Generated %d execution steps (placeholder)", len(steps))
+	return steps
+}
+
+// GetDeclaredOutputFiles returns empty list - custom engines define their own outputs
+func (e *CustomEngine) GetDeclaredOutputFiles() []string {
+	return []string{}
+}
+
+// RenderMCPConfig provides no MCP configuration for custom engines
+// Custom engines must implement MCP support themselves if needed
+func (e *CustomEngine) RenderMCPConfig(yaml *strings.Builder, tools map[string]any, mcpTools []string, workflowData *WorkflowData) {
+	customLog.Print("Custom engine does not provide built-in MCP configuration")
+	// No-op - custom engines don't provide MCP configuration by default
+}
+
+// convertStepToYAML converts a step map to YAML format for GitHub Actions
+func (e *CustomEngine) convertStepToYAML(stepMap map[string]any) (string, error) {
+	return ConvertStepToYAML(stepMap)
+}