 Southwick has also been the director or managing director of The Market Stars Group, ICE Events Pty Ltd and David James Investments Pty Ltd.

Southwick was the Liberal candidate for the Division of Melbourne Ports in the 2004 federal election, achieving a swing of almost 2 points against the incumbent MP Michael Danby.In the 2006 state election he was a Liberal candidate for the Southern Metropolitan Region, narrowly missing out on being elected.He was elected in 2010 as the Member for Caulfield and delivered his first speech on 8 February 2011.