diff --git a/mercurial/configitems.py b/mercurial/configitems.py
--- a/mercurial/configitems.py
+++ b/mercurial/configitems.py
@@ -1601,6 +1601,14 @@
     experimental=True,
 )
 coreconfigitem(
+    b'partial-merge-tools',
+    br'.*\.args',
+    default=b"$local $base $other",
+    generic=True,
+    priority=-1,
+    experimental=True,
+)
+coreconfigitem(
     b'merge-tools',
     b'.*',
     default=None,
diff --git a/mercurial/filemerge.py b/mercurial/filemerge.py
--- a/mercurial/filemerge.py
+++ b/mercurial/filemerge.py
@@ -1120,7 +1120,7 @@
 def _run_partial_resolution_tools(repo, local, other, base):
     """Runs partial-resolution tools on the three inputs and updates them."""
     ui = repo.ui
-    # Tuples of (order, name, executable path)
+    # Tuples of (order, name, executable path, args)
     tools = []
     seen = set()
     section = b"partial-merge-tools"
@@ -1136,7 +1136,8 @@
         if is_match:
             order = ui.configint(section, b'%s.order' % name, 0)
             executable = ui.config(section, b'%s.executable' % name, name)
-            tools.append((order, name, executable))
+            args = ui.config(section, b'%s.args' % name)
+            tools.append((order, name, executable, args))
 
     if not tools:
         return
@@ -1152,11 +1153,21 @@
     with _maketempfiles(files) as temppaths:
         localpath, basepath, otherpath = temppaths
 
-        for order, name, executable in tools:
+        for order, name, executable, args in tools:
             cmd = procutil.shellquote(executable)
-            # TODO: Allow the user to configure the command line using
-            # $local, $base, $other.
-            cmd = b'%s %s %s %s' % (cmd, localpath, basepath, otherpath)
+            replace = {
+                b'local': localpath,
+                b'base': basepath,
+                b'other': otherpath,
+            }
+            args = util.interpolate(
+                br'\$',
+                replace,
+                args,
+                lambda s: procutil.shellquote(util.localpath(s)),
+            )
+
+            cmd = b'%s %s' % (cmd, args)
             r = ui.system(cmd, cwd=repo.root, blockedtag=b'partial-mergetool')
             if r:
                 raise error.StateError(
diff --git a/tests/test-merge-partial-tool.t b/tests/test-merge-partial-tool.t
--- a/tests/test-merge-partial-tool.t
+++ b/tests/test-merge-partial-tool.t
@@ -207,3 +207,35 @@
   c
   d
   e3
+
+Test that arguments get passed as expected.
+
+  $ cat >> "$TESTTMP/log-args.sh" <<'EOF'
+  > #!/bin/sh
+  > echo "$@" > args.log
+  > EOF
+  $ chmod +x "$TESTTMP/log-args.sh"
+  $ cat >> "$HGRCPATH" <<EOF
+  > [partial-merge-tools]
+  > log-args.executable=$TESTTMP/log-args.sh
+  > EOF
+  $ hg up -C 2
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg merge 1
+  merging file
+  warning: conflicts while merging file! (edit, then use 'hg resolve --mark')
+  0 files updated, 0 files merged, 0 files removed, 1 files unresolved
+  use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
+  [1]
+  $ cat args.log
+  */hgmerge-*/file~local */hgmerge-*/file~base */hgmerge-*/file~other (glob)
+  $ hg up -C 2
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg merge 1 --config partial-merge-tools.log-args.args='--other $other $base --foo --local $local --also-other $other'
+  merging file
+  warning: conflicts while merging file! (edit, then use 'hg resolve --mark')
+  0 files updated, 0 files merged, 0 files removed, 1 files unresolved
+  use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
+  [1]
+  $ cat args.log
+  --other */hgmerge-*/file~other */hgmerge-*/file~base --foo --local */hgmerge-*/file~local --also-other */hgmerge-*/file~other (glob)