[citation needed] Born in Sydney in 1949, St. Clair was educated at Sydney Church of England Grammar School (Shore) and spent his early life as a small businessman in the timber industry as a merchant, sawmiller and truck driver before becoming involved in politics in the 1980s.

He contested and won the subsequent election and served on a number of parliamentary committees during the 39th Parliament.

In 2001, St. Clair was defeated by independent Tony Windsor on a 21-point swing, ending a nearly 80-year hold on the seat by the Nationals.

In March 2006, St. Clair was appointed Chief Executive of the Australian Trucking Association until his retirement in 2015.

St. Clair moved to the Margaret River area of Western Australia and continued his association with the Nationals, becoming Chairman of the Vasse Branch in 2016.