Carlsson was a member of the Riksdag from 1965 to 1996 representing the constituency of Stockholm County (until 1970 in the lower house). He served as Minister of Education from 1969 to 1973, as Minister of Housing in 1973 and again from 1974 to 1976, and as Minister of Environmental affairs from 1985 to 1986. He served as Deputy Prime Minister from 1982 to 1986, and assumed office as Prime Minister of Sweden upon the assassination of Prime Minister Olof Palme in 1986.