In July 2005, Cobb was appointed to the ministry as Minister for Citizenship and Multicultural Affairs, but soon after was reshuffled to the community services portfolio.

After Parkes was dramatically altered in a redistribution, Cobb ran for the neighbouring seat of Calare at the 2007 election after the popular independent member Peter Andren retired.

He was chosen by new Opposition leader Brendan Nelson to be a member of the shadow ministry, as the spokesperson on regional development and water security.

[5] He was re-elected at the 2010 election and in September 2010 was appointed Shadow Minister for Agriculture and Food Security by Opposition leader, Tony Abbott.

[7] On 27 February 2016, Cobb announced that he was retiring from politics and would not re-contest the Division of Calare in the 2016 Australian federal election.