He was the leader of the Social Democratic Party from 1969-1986 to his death and Prime Minister of Sweden from 1969 - 1976 and 1982 - 1986 . Palme was the leader of the Swedish Social Democratic Party and two-term Prime Minister of Sweden , heading a Privy Council Government from 1969 to 1976 and a cabinet government from 1982 until his assassination in 1986 .