He was Finland"s Minister of Defence in Jyrki Katainen"s cabinet between 2011-2012. He worked as a reporter for the newspaper Vasabladet from 1989 to 1993 before acting as a research assistant for the Swedish People"s Party. He served as a Special Adviser successively to the Ministers of Transport, European Affairs and Foreign Trade, Interior, and Defence from 1994 to 2000.
He was Deputy Editor-in-Chief and a leader writer for the newspaper Åbo Underrättelser from 2000 to 2005.
He then served as State Secretary to the Minister of the Environment from 2005 to 2007. Wallin was appointed Minister of the Environment and Minister at the Ministry for Foreign Affairs responsible for Nordic Cooperation by President Tarja Halonen on 29 December 2006.
He succeeded January-Erik Enestam, who was also Wallin"s predecessor as chairman of the Swedish People"s Party. On 22 June 2011 he was appointed the Minister of Defence.
He gave up the position in 2012, when he was succeeded by Carl Haglund as Defence Minister as well as the chairman of the party.