In the 2005 election, Foss was a candidate for the National Party, standing in the Tukituki electorate and being ranked 44th on the party list. He won the Tukituki seat and entered Parliament. He was returned to the 49th Parliament, holding the Tukituki seat, in the 2008 election.
On 7 June 2011 Foss was announced to be the new Minister of Civil Defence, replacing John Carter who leaves to take up a High Commissioners post in the Cook Islands. Foss also picks up the Racing and Senior Citizens portfolios but will remain a Minister outside Cabinet for the remainder of the 49th New Zealand Parliament.