diff --git a/mercurial/dispatch.py b/mercurial/dispatch.py
--- a/mercurial/dispatch.py
+++ b/mercurial/dispatch.py
@@ -37,6 +37,7 @@ from . import (
     revset,
     templatefilters,
     templatekw,
+    templater,
     ui as uimod,
     util,
 )
@@ -768,6 +769,7 @@ extraloaders = [
     ('filesetpredicate', fileset, 'loadpredicate'),
     ('revsetpredicate', revset, 'loadpredicate'),
     ('templatefilter', templatefilters, 'loadfilter'),
+    ('templatefunc', templater, 'loadfunction'),
     ('templatekeyword', templatekw, 'loadkeyword'),
 ]
 
diff --git a/mercurial/registrar.py b/mercurial/registrar.py
--- a/mercurial/registrar.py
+++ b/mercurial/registrar.py
@@ -216,3 +216,29 @@ class templatefilter(_templateregistrarb
 
     Otherwise, explicit 'templatefilters.loadkeyword()' is needed.
     """
+
+class templatefunc(_templateregistrarbase):
+    """Decorator to register template function
+
+    Usage::
+
+        templatefunc = registrar.templatefunc()
+
+        @templatefunc('myfunc(arg1, arg2[, arg3])')
+        def myfuncfunc(context, mapping, args):
+            '''Explanation of this template function ....
+            '''
+            pass
+
+    The first string argument is used also in online help.
+
+    'templatefunc' instance in example above can be used to
+    decorate multiple functions.
+
+    Decorated functions are registered automatically at loading
+    extension, if an instance named as 'templatefunc' is used for
+    decorating in extension.
+
+    Otherwise, explicit 'templater.loadfunction()' is needed.
+    """
+    _getname = _funcregistrarbase._parsefuncdecl
diff --git a/mercurial/templater.py b/mercurial/templater.py
--- a/mercurial/templater.py
+++ b/mercurial/templater.py
@@ -1069,5 +1069,11 @@ def stylemap(styles, paths=None):
 
     raise RuntimeError("No hgweb templates found in %r" % paths)
 
+def loadfunction(ui, extname, registrarobj):
+    """Load template function from specified registrarobj
+    """
+    for name, func in registrarobj._table.iteritems():
+        funcs[name] = func
+
 # tell hggettext to extract docstrings from these functions:
 i18nfunctions = funcs.values()
diff --git a/tests/test-command-template.t b/tests/test-command-template.t
--- a/tests/test-command-template.t
+++ b/tests/test-command-template.t
@@ -3693,3 +3693,26 @@ utf8 filter:
   [255]
 
   $ cd ..
+
+Test that template function in extension is registered as expected
+
+  $ cd a
+
+  $ cat <<EOF > $TESTTMP/customfunc.py
+  > from mercurial import registrar
+  > 
+  > templatefunc = registrar.templatefunc()
+  > 
+  > @templatefunc('custom()')
+  > def custom(context, mapping, args):
+  >     return 'custom'
+  > EOF
+  $ cat <<EOF > .hg/hgrc
+  > [extensions]
+  > customfunc = $TESTTMP/customfunc.py
+  > EOF
+
+  $ hg log -r . -T "{custom()}\n" --config customfunc.enabled=true
+  custom
+
+  $ cd ..