While a student at the Paisley College of Technology he was deputy president of the student union. Rennie ran the Scottish Young Liberal Democrats (later reformed as Liberal Youth Scotland) and after graduation went on to work for the English Liberal Democrats in Cornwall. He then went on to work for the Liberal Democrats' campaigns department, and was the successful agent in the 1993 Christchurch by-election in Dorset. After managing the party's campaigns in the South West England region, securing the return of a sizeable number of new MPs in the 1997 General Election, he moved back to Scotland where he was Chief Executive of the Scottish Liberal Democrats from 1997 to 1999, and then the party's Chief of Staff in the new Scottish Parliament from 1999–2001. McEwan Purvis: 2001–2006 From 2001 to 2006 he worked for the small Scottish communications firm McEwan Purvis as an account director helping advise businesses and charities such as the Royal Society of Chemistry and Asthma UK. During his time at McEwan Purvis, Rennie was a press adviser to Fife Council's Liberal Democrat Opposition Group and a member of the Dunfermline Focus editorial team, working with Dunfermline's Lib Dem councillors on local issues. Member of Parliament: 2006–2010 After Labour MP Rachel Squire died, Rennie stood in the Dunfermline and West Fife by-election on 9 February 2006 and overturned a Labour majority of 11,800 to win the seat with a swing to his party of 16.24%. In the House of Commons, he was a member of the Liberal Democrat defence spokesperson team, chair of their parliamentary campaigns unit, and a member of the Commons Defence Select Committee. During his time as an MP, he campaigned on local constituency issues such as abolishing the bridge tolls, banning sex offenders from being driving instructors in 2008, improvements to cancer services at Queen Margaret Hospital, and local jobs (including at Longannet Power Station and Rosyth Dockyard). In the General Election of 6 May 2010, Rennie lost his seat to the Labour candidate Thomas Docherty. Special Adviser and consultant: 2010–2011 He was then for a time Special Adviser to the new Liberal Democrat Scottish Secretary Michael Moore MP. Elected MSP and Leader of the Scottish Liberal Democrats: since 2011 Rennie returned to front-line politics as an MSP when he won a regional list seat for the Liberal Democrats in the Scottish Parliament's Mid Scotland and Fife region at the