Hamm, a graduate of the University of King's College, was a family doctor in his hometown of New Glasgow, Nova Scotia, and the president of the Nova Scotia Medical Society. He entered politics in 1993, becoming the Member of the Legislative Assembly for the riding of Pictou Centre.
Hamm became leader of the Progressive Conservative Party of Nova Scotia in 1995. His party won 14 seats in the 1998 provincial election and held the balance of power in a minority government where both the Liberal Party and the New Democratic Party had nineteen seats. His party defeated the government on a budget vote in May 1999, in the subsequent election on July 27, 1999, Hamm became the new premier, winning 29 of the 52 seats in the provincial legislature.
Since taking office, Hamm has been selling or closing many government-owned industries such as Sydney Steel. He has invested more in education and health care, and has implemented some tax cuts.
In 2001 Hamm was at odds with the Nova Scotia Government Employees Union, trying to legislate nurses back to work after a long and bitter strike.
In the 2003 election Hamm and his conservatives were reelected to a minority government. The main issue in that election was the increasing cost of car insurance and whether Nova Scotia should begin to allow general Sunday shopping. Due to the minority government Hamm's government may have to compromise their position on both of these issues. Hamm is opposed to Sunday shopping and a public insurance system.