Following the parliamentary election held on 17 April 2011, Katainen was elected Prime Minister by the new parliament and assumed office on 22 June 2011. His centre-right National Coalition Party became the largest party for the first time in the history of Finland. Following government-forming negotiations, Katainen was elected Prime Minister by the Finnish Parliament, and his government of six parties (National Coalition Party, Social Democratic Party of Finland, Left Alliance (Finland), Green League, Swedish People's Party of Finland and Christian Democrats (Finland) ) was formally appointed by President Tarja Halonen on 22 June 2011.