After college, Rennie was a Liberal Democrat election campaigner and official before working as a public relations consultant in the private sector.

He briefly served as a Special Government Adviser for the Liberal Democrat Scottish Secretaries of State Danny Alexander and Michael Moore at the Scotland Office.

Rennie was re-elected in the 2021 Scottish Parliament election, but resigned as Lib Dem leader two months later and was replaced by Alex Cole-Hamilton.

Rennie went to Bell Baxter High School in Cupar, Fife, before going to Paisley College of Technology, where he graduated with a BSc in biology.

[4] Rennie was one of the 50 MPs who ran a mile to raise money for Sport Relief[5] finishing close behind the winner, David Davies.

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 as an MP, he campaigned on local constituency issues such as abolishing the bridge tolls, banning sex offenders from being driving instructors in 2008,[7] improvements to cancer services at Queen Margaret Hospital, and local jobs (including at Longannet Power Station and Rosyth Dockyard).

He vowed to stand up to the "SNP bulldozer" majority, and refused to distance his party from the UK Liberal Democrats.