diff --git a/trac/wiki/api.py b/trac/wiki/api.py
--- a/trac/wiki/api.py
+++ b/trac/wiki/api.py
@@ -82,9 +82,17 @@
     def render_macro(req, name, content):
         """Return the HTML output of the macro (deprecated)"""
 
-    def expand_macro(formatter, name, content):
+    def expand_macro(formatter, name, content, args={}):
         """Called by the formatter when rendering the parsed wiki text.
 
+        `content` is the content of the macro call. When called using macro
+        syntax (`[[Macro(content)]]`), this is the string contained between
+        parentheses, usually containing macro arguments. When called using wiki
+        processor syntax (`{{{!#Macro ...}}}`), it is the content of the
+        processor block, that is, the text starting on the line following the
+        macro name. In this case, `args` contains the named arguments passed on
+        the same line as the macro name.
+
         (since 0.11)
         """
 
diff --git a/trac/wiki/formatter.py b/trac/wiki/formatter.py
--- a/trac/wiki/formatter.py
+++ b/trac/wiki/formatter.py
@@ -34,6 +34,7 @@
 from trac.resource import get_relative_resource, get_resource_url
 from trac.wiki.api import WikiSystem, parse_args
 from trac.wiki.parser import WikiParser
+from trac.util import arity
 from trac.util.text import exception_to_unicode, shorten_line, to_unicode, \
                            unicode_quote, unicode_quote_plus
 from trac.util.html import TracHTMLSanitizer
@@ -175,8 +176,12 @@
     def _macro_processor(self, text):
         self.env.log.debug('Executing Wiki macro %s by provider %s'
                            % (self.name, self.macro_provider))
-        return self.macro_provider.expand_macro(self.formatter, self.name,
-                                                text)
+        if arity(self.macro_provider.expand_macro) == 5:
+            return self.macro_provider.expand_macro(self.formatter, self.name,
+                                                    text, self.args)
+        else:
+            return self.macro_provider.expand_macro(self.formatter, self.name,
+                                                    text)
 
     def _mimeview_processor(self, text):
         return Mimeview(self.env).render(self.formatter.context,
@@ -796,7 +801,7 @@
             match = WikiParser._processor_re.match(line)
             if match:
                 name = match.group(1)
-                args = WikiParser._processor_param_re.split(line[len(name):])
+                args = WikiParser._processor_param_re.split(line[2+len(name):])
                 del args[::3]
                 keys = [str(k) for k in args[::2]] # used as keyword parameters
                 values = [(v and v[0] in '"\'' and [v[1:-1]] or [v])[0]