Claim: Prime Minister Kalevi Sorsa, of the Social Democratic Party (Finland's oldest active political party, served in office from 6 May 1983 – 30 April 1987.
Evidence: Prime Minister Kalevi Sorsa 19 February 1982 6 May 1983 Sorsa's fourth cabinet was the 63rd government of Finland, which existed for 1 456 days, from 6 May 1983 to 30 April 1987. The government's Prime Minister was Kalevi Sorsa. Social Democratic Party
Centre Party
Swedish People's Party
Rural Party Founded in 1899, the SDP is Finland's oldest active political party. 
Founded in 1899, the SDP is Finland's oldest active political party. 6 May 1983 30 April 1987 Kalevi Sorsa Social Democratic Party
Centre Party
Swedish People's Party
Rural Party The government's Prime Minister was Kalevi Sorsa.