He was a Labor Party member of the New South Wales Legislative Assembly from 2007 until 2011, representing the electorate of Wollondilly.
His decision to join the Labor Party was opposed by other councillors who called on him to resign the mayoralty.
[4] Numerous Wollondilly councillors also expressed opposition to Costa's 2008 support for a new commuter car park at Macarthur Railway Station,[5][6] and for a 2009 proposal for an AGL power station near Appin.
[1][11] In 2011 he lost Wollondilly to Liberal Jai Rowell as part of an anti-Labor landslide in that year.
Later moving to the NSW North Coast, Costa was the unsuccessful Labor candidate for the Federal seat of Lyne in the 2019 election.