diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3892782529..29b890fe4b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -74,6 +74,10 @@ to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 * New `merge-tools.<TOOL>.conflict-marker-style` config option to override the
   conflict marker style used for a specific merge tool.
 
+* New `merge-tools.<TOOL>.merge-tool-error-status-on-conflict` config option to
+  allow a merge tool to exit with a status between 1 and 127 to indicate that
+  not all conflicts were resolved.
+
 * `jj simplify-parents` now supports configuring the default revset when no
    `--source` or `--revisions` arguments are provided with the
    `revsets.simplify-parents` config.
diff --git a/cli/src/config-schema.json b/cli/src/config-schema.json
index 3d1202463c..87c9449872 100644
--- a/cli/src/config-schema.json
+++ b/cli/src/config-schema.json
@@ -400,6 +400,11 @@
                             "type": "string"
                         }
                     },
+                    "merge-tool-error-status-on-conflict": {
+                      "type": "boolean",
+                      "description": "If true, an exit status between 1 and 127 indicates that the conflict was only partially resolved. See https://martinvonz.github.io/jj/latest/config/#editing-conflict-markers-with-a-tool-or-a-text-editor",
+                      "default": false
+                    },
                     "merge-tool-edits-conflict-markers": {
                         "type": "boolean",
                         "description": "Whether to populate the output file with conflict markers before starting the merge tool. See https://martinvonz.github.io/jj/latest/config/#editing-conflict-markers-with-a-tool-or-a-text-editor",
diff --git a/cli/src/merge_tools/external.rs b/cli/src/merge_tools/external.rs
index 8f7689b737..78db125662 100644
--- a/cli/src/merge_tools/external.rs
+++ b/cli/src/merge_tools/external.rs
@@ -58,6 +58,11 @@ pub struct ExternalMergeTool {
     /// `$left`, `$right`, `$base`, and `$output` are replaced with
     /// paths to the corresponding files.
     pub merge_args: Vec<String>,
+    /// If false (default), any exit status from the merge tool other than 0
+    /// will cause `jj resolve` to fail. If true, then any status between 1 and
+    /// 127 can be used to indicate that the conflict was not fully resolved,
+    /// and the output file should contain conflict markers.
+    pub merge_tool_error_status_on_conflict: bool,
     /// If false (default), the `$output` file starts out empty and is accepted
     /// as a full conflict resolution as-is by `jj` after the merge tool is
     /// done with it. If true, the `$output` file starts out with the
@@ -93,6 +98,7 @@ impl Default for ExternalMergeTool {
             diff_args: ["$left", "$right"].map(ToOwned::to_owned).to_vec(),
             edit_args: ["$left", "$right"].map(ToOwned::to_owned).to_vec(),
             merge_args: vec![],
+            merge_tool_error_status_on_conflict: false,
             merge_tool_edits_conflict_markers: false,
             conflict_marker_style: None,
             diff_invocation_mode: DiffToolMode::Dir,
@@ -150,6 +156,11 @@ pub enum ExternalToolError {
     },
     #[error("Tool exited with {exit_status} (run with --debug to see the exact invocation)")]
     ToolAborted { exit_status: ExitStatus },
+    #[error(
+        "Tool exited with {exit_status}, but did not produce valid conflict markers (run with \
+         --debug to see the exact invocation)"
+    )]
+    InvalidConflictMarkers { exit_status: ExitStatus },
     #[error("I/O error")]
     Io(#[source] std::io::Error),
 }
@@ -218,7 +229,13 @@ pub fn run_mergetool_external(
             tool_binary: editor.program.clone(),
             source: e,
         })?;
-    if !exit_status.success() {
+
+    // Check whether the exit status implies that there should be conflict markers
+    let exit_status_implies_conflict = editor.merge_tool_error_status_on_conflict
+        && !exit_status.success()
+        && exit_status.code().is_some_and(|code| code <= 127);
+
+    if !exit_status.success() && !exit_status_implies_conflict {
         return Err(ConflictResolveError::from(ExternalToolError::ToolAborted {
             exit_status,
         }));
@@ -230,7 +247,7 @@ pub fn run_mergetool_external(
         return Err(ConflictResolveError::EmptyOrUnchanged);
     }
 
-    let new_file_ids = if editor.merge_tool_edits_conflict_markers {
+    let new_file_ids = if editor.merge_tool_edits_conflict_markers || exit_status_implies_conflict {
         conflicts::update_from_content(
             &file_merge,
             tree.store(),
@@ -246,6 +263,17 @@ pub fn run_mergetool_external(
             .block_on()?;
         Merge::normal(new_file_id)
     };
+
+    // If the exit status indicated there should be conflict markers but there
+    // weren't any, it's likely that the tool generated incorrect conflict markers,
+    // so we need to inform the user. If we didn't treat this as an error, the user
+    // might think the conflict was resolved successfully.
+    if exit_status_implies_conflict && new_file_ids.is_resolved() {
+        return Err(ConflictResolveError::ExternalTool(
+            ExternalToolError::InvalidConflictMarkers { exit_status },
+        ));
+    }
+
     let new_tree_value = match new_file_ids.into_resolved() {
         Ok(new_file_id) => Merge::normal(TreeValue::File {
             id: new_file_id.unwrap(),
diff --git a/cli/src/merge_tools/mod.rs b/cli/src/merge_tools/mod.rs
index d7be4f55fa..2b279f2ed0 100644
--- a/cli/src/merge_tools/mod.rs
+++ b/cli/src/merge_tools/mod.rs
@@ -401,6 +401,7 @@ mod tests {
                     "$right",
                 ],
                 merge_args: [],
+                merge_tool_error_status_on_conflict: false,
                 merge_tool_edits_conflict_markers: false,
                 conflict_marker_style: None,
             },
@@ -429,6 +430,7 @@ mod tests {
                     "$right",
                 ],
                 merge_args: [],
+                merge_tool_error_status_on_conflict: false,
                 merge_tool_edits_conflict_markers: false,
                 conflict_marker_style: None,
             },
@@ -469,6 +471,7 @@ mod tests {
                     "$right",
                 ],
                 merge_args: [],
+                merge_tool_error_status_on_conflict: false,
                 merge_tool_edits_conflict_markers: false,
                 conflict_marker_style: None,
             },
@@ -493,6 +496,7 @@ mod tests {
                     "$right",
                 ],
                 merge_args: [],
+                merge_tool_error_status_on_conflict: false,
                 merge_tool_edits_conflict_markers: false,
                 conflict_marker_style: None,
             },
@@ -516,6 +520,7 @@ mod tests {
                     "$right",
                 ],
                 merge_args: [],
+                merge_tool_error_status_on_conflict: false,
                 merge_tool_edits_conflict_markers: false,
                 conflict_marker_style: None,
             },
@@ -545,6 +550,7 @@ mod tests {
                     "$right",
                 ],
                 merge_args: [],
+                merge_tool_error_status_on_conflict: false,
                 merge_tool_edits_conflict_markers: false,
                 conflict_marker_style: None,
             },
@@ -572,6 +578,7 @@ mod tests {
                     "$right",
                 ],
                 merge_args: [],
+                merge_tool_error_status_on_conflict: false,
                 merge_tool_edits_conflict_markers: false,
                 conflict_marker_style: None,
             },
@@ -593,6 +600,7 @@ mod tests {
                     "$right",
                 ],
                 merge_args: [],
+                merge_tool_error_status_on_conflict: false,
                 merge_tool_edits_conflict_markers: false,
                 conflict_marker_style: None,
             },
@@ -646,6 +654,7 @@ mod tests {
                     "$right",
                     "$output",
                 ],
+                merge_tool_error_status_on_conflict: false,
                 merge_tool_edits_conflict_markers: false,
                 conflict_marker_style: None,
             },
@@ -694,6 +703,7 @@ mod tests {
                     "$right",
                     "$output",
                 ],
+                merge_tool_error_status_on_conflict: false,
                 merge_tool_edits_conflict_markers: false,
                 conflict_marker_style: None,
             },
@@ -723,6 +733,7 @@ mod tests {
                     "$right",
                     "$output",
                 ],
+                merge_tool_error_status_on_conflict: false,
                 merge_tool_edits_conflict_markers: false,
                 conflict_marker_style: None,
             },
@@ -755,6 +766,7 @@ mod tests {
                     "$right",
                     "$output",
                 ],
+                merge_tool_error_status_on_conflict: false,
                 merge_tool_edits_conflict_markers: false,
                 conflict_marker_style: None,
             },
diff --git a/docs/config.md b/docs/config.md
index 9d7f6b335c..c43d3a5344 100644
--- a/docs/config.md
+++ b/docs/config.md
@@ -841,9 +841,19 @@ merge-tool-edits-conflict-markers = true    # See below for an explanation
 ### Editing conflict markers with a tool or a text editor
 
 By default, the merge tool starts with an empty output file. If the tool puts
-anything into the output file, and exits with the 0 exit code,
-`jj` assumes that the conflict is fully resolved. This is appropriate for most
-graphical merge tools.
+anything into the output file and exits with the 0 exit code,
+`jj` assumes that the conflict is fully resolved, while if the tool exits with
+a non-zero exit code, `jj` assumes that the merge should be cancelled.
+This is appropriate for most graphical merge tools.
+
+For merge tools which try to automatically resolve conflicts without user
+input, this behavior may not be desired. These tools may require setting
+the `merge-tools.TOOL.merge-tool-error-status-on-conflict = true` option.
+With this option set, an exit code between 1 and 127 indicates that only some
+of the conflicts were resolved, and the output file should contain conflict
+markers. If a merge tool produces output using Git's "diff3" conflict style,
+`jj` should be able to parse it correctly, so many Git merge drivers should be
+usable with `jj` as well.
 
 Some tools (e.g. `vimdiff`) can present a multi-way diff but don't resolve
 conflict themselves. When using such tools, `jj`