He was a Labor Party member of the Victorian Legislative Council from 1999 to 2020, representing Melbourne Province (1999–2006) and then the South Eastern Metropolitan Region (2006–2020) .

[2] Jennings studied at Beaufort High School and Monash University, attaining degrees in arts and social work.

On 25 May 2016, the Legislative Council passed a contempt motion against Jennings, effectively suspending him from parliament for up to six months, unless he released documents to the Upper House relating to the Victorian Comprehensive Cancer Centre.

The premier, Daniel Andrews, said the Labor movement was "more confident, more courageous and more compasionate" because of Jennings.

On the 23 April 2020, former MP and member of the party's Left faction Lee Tarlamis was sworn in as Jennings's replacement.