diff --git a/Documentation/config/gui.txt b/Documentation/config/gui.txt
index 171be774d243fd..e63d0b46e7c421 100644
--- a/Documentation/config/gui.txt
+++ b/Documentation/config/gui.txt
@@ -55,3 +55,7 @@ gui.blamehistoryctx::
 	linkgit:gitk[1] for the selected commit, when the `Show History
 	Context` menu item is invoked from 'git gui blame'. If this
 	variable is set to zero, the whole history is shown.
+
+gui.mergeToolFromConfig::
+	If true, allow to call the merge tool configured in gitconfig
+	in git gui directly.
\ No newline at end of file
diff --git a/git-gui/lib/mergetool.tcl b/git-gui/lib/mergetool.tcl
index e688b016ef6c9d..fbd0889612a302 100644
--- a/git-gui/lib/mergetool.tcl
+++ b/git-gui/lib/mergetool.tcl
@@ -272,8 +272,15 @@ proc merge_resolve_tool2 {} {
 		}
 	}
 	default {
-		error_popup [mc "Unsupported merge tool '%s'" $tool]
-		return
+		if {[is_config_true gui.mergetoolfromconfig]} {
+			set path [get_config mergetool.$tool.path]
+			set cmdline_config [get_config mergetool.$tool.cmd]
+			set cmdline_substituted [subst -nobackslashes -nocommands $cmdline_config]
+			set cmdline [lreplace $cmdline_substituted 0 0 $path]
+		} else {
+			error_popup [mc "Unsupported merge tool '%s'" $tool]
+			return
+		}
 	}
 	}