In May 2011 he was elected Member of the Scottish Parliament for Mid Scotland and Fife. 
According to a biographical note on the McEwan Purvis website:
- Willie has extensive experience in public affairs and public relations. Before joining McEwan Purvis, he handled parliamentary affairs for the Royal Society of Chemistry and was Campaigns Manager for National Asthma Campaign Scotland. Willie was Chief Executive and Chief of Staff for the Scottish Liberal Democrats between 1997 and 2001.