Couchepin first entered politics in 1968, when he was elected to the Communal Council in his hometown of Martigny. He went on to become deputy mayor (1976) and then mayor(1984) of the city. By this time he was already active at the federal level as a member of the National Council, to which he was elected in 1979. He led his party's contingent in Parliament from 1989 to 1996, and continued to serve as mayor of Martigny until 1998, when he was elected to serve on the powerful Federal Council, the seven-member body that directs Swiss politics.
Upon his election to the Federal Council, Couchepin became minister for economic affairs, with responsibility for the offices of labor, professional education, trade, and agriculture. He was also the Swiss representative to the World Trade Organization (WTO) and was a governor of both the World Bank and the European Bank for Reconstruction and Development (EBRD). After serving as vice president for a year, Couchepin was elected to the presidency of the Swiss Confederation on 4 December 2002. On 1 January 2003, his portfolio on the Federal Council (on which the Swiss president continues to serve) was changed to the Department of Home Affairs, with responsibility for health, social security, education, research, and cultural matters.