diff --git a/internal/beads/beads.go b/internal/beads/beads.go
index 139f8ce9..3384d611 100644
--- a/internal/beads/beads.go
+++ b/internal/beads/beads.go
@@ -1118,3 +1118,28 @@ func (b *Beads) GetRoleConfig(roleBeadID string) (*RoleConfig, error) {
 
 	return ParseRoleConfig(issue.Description), nil
 }
+
+// FindMRForBranch searches for an existing merge-request bead for the given branch.
+// Returns the MR bead if found, nil if not found.
+// This enables idempotent `gt done` - if an MR already exists, we skip creation.
+func (b *Beads) FindMRForBranch(branch string) (*Issue, error) {
+	// List all merge-request beads (open status only - closed MRs are already processed)
+	issues, err := b.List(ListOptions{
+		Status: "open",
+		Type:   "merge-request",
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	// Search for one matching this branch
+	// MR description format: "branch: <branch>\ntarget: ..."
+	branchPrefix := "branch: " + branch + "\n"
+	for _, issue := range issues {
+		if strings.HasPrefix(issue.Description, branchPrefix) {
+			return issue, nil
+		}
+	}
+
+	return nil, nil
+}
diff --git a/internal/cmd/done.go b/internal/cmd/done.go
index 2724fa0d..2767f857 100644
--- a/internal/cmd/done.go
+++ b/internal/cmd/done.go
@@ -153,29 +153,43 @@ func runDone(cmd *cobra.Command, args []string) error {
 			}
 		}
 
-		// Build MR bead title and description
-		title := fmt.Sprintf("Merge: %s", issueID)
-		description := fmt.Sprintf("branch: %s\ntarget: %s\nsource_issue: %s\nrig: %s",
-			branch, target, issueID, rigName)
-		if worker != "" {
-			description += fmt.Sprintf("\nworker: %s", worker)
-		}
-
-		// Create MR bead (ephemeral wisp - will be cleaned up after merge)
-		mrIssue, err := bd.Create(beads.CreateOptions{
-			Title:       title,
-			Type:        "merge-request",
-			Priority:    priority,
-			Description: description,
-		})
+		// Check if MR bead already exists for this branch (idempotency)
+		existingMR, err := bd.FindMRForBranch(branch)
 		if err != nil {
-			return fmt.Errorf("creating merge request bead: %w", err)
+			style.PrintWarning("could not check for existing MR: %v", err)
+			// Continue with creation attempt - Create will fail if duplicate
 		}
-		mrID = mrIssue.ID
 
-		// Success output
-		fmt.Printf("%s Work submitted to merge queue\n", style.Bold.Render("✓"))
-		fmt.Printf("  MR ID: %s\n", style.Bold.Render(mrID))
+		if existingMR != nil {
+			// MR already exists - use it instead of creating a new one
+			mrID = existingMR.ID
+			fmt.Printf("%s MR already exists (idempotent)\n", style.Bold.Render("✓"))
+			fmt.Printf("  MR ID: %s\n", style.Bold.Render(mrID))
+		} else {
+			// Build MR bead title and description
+			title := fmt.Sprintf("Merge: %s", issueID)
+			description := fmt.Sprintf("branch: %s\ntarget: %s\nsource_issue: %s\nrig: %s",
+				branch, target, issueID, rigName)
+			if worker != "" {
+				description += fmt.Sprintf("\nworker: %s", worker)
+			}
+
+			// Create MR bead (ephemeral wisp - will be cleaned up after merge)
+			mrIssue, err := bd.Create(beads.CreateOptions{
+				Title:       title,
+				Type:        "merge-request",
+				Priority:    priority,
+				Description: description,
+			})
+			if err != nil {
+				return fmt.Errorf("creating merge request bead: %w", err)
+			}
+			mrID = mrIssue.ID
+
+			// Success output
+			fmt.Printf("%s Work submitted to merge queue\n", style.Bold.Render("✓"))
+			fmt.Printf("  MR ID: %s\n", style.Bold.Render(mrID))
+		}
 		fmt.Printf("  Source: %s\n", branch)
 		fmt.Printf("  Target: %s\n", target)
 		fmt.Printf("  Issue: %s\n", issueID)