Barnett was born in Belper, Derbyshire, England, and briefly attended Trescobeas County Secondary School (in Falmouth, Cornwall).
Prior to entering politics, Barnett was the owner of a caravan park in Rockingham, one of Perth's southern suburbs.
[1] He joined the Labor Party in 1970, and at the 1974 state election successfully contested the newly created seat of Rockingham, narrowly defeating the Liberal candidate.
However, when Labor won government at the 1983 election, Barnett was not elevated to cabinet, but instead made chairman of committees in the Legislative Assembly.
From 2004 to 2008, Barnett served as chairman of the Fire and Emergency Services Authority (FESA), a state government agency.