A member of the Christian Democratic Union (CDU), Heinemann entered the Diet of North Rhine-Westphalia in 1947 and was its minister of justice during 1947–1948. Although not a member of the Bundestag, he was nevertheless appointed federal minister of the interior in Chancellor Konrad Adenauer's government in September 1949, a tactical move to include the Protestant wing of the CDU in the cabinet. Heinemann resigned from office in October 1950 after a dispute with Adenauer over the chancellor's plan to rearm West Germany. Heinemann left the CDU in 1952 and founded the All-German Peoples' Party, which suffered a major electoral defeat in 1957.
After the defeat, Heinemann joined the Social Democratic Party (SPD) and entered the Bundestag in 1957. He subsequently served as federal minister of justice in the coalition cabinet of Kurt-Georg Kiesinger from 1966 until his election as president in March 1969; he remained in that office until June 1974. As the so-called citizen president, Heinemann, in his public speeches, repeatedly sought to further develop values such as democracy and individual freedom in West Germany. During several state visits to neighboring countries, he strove to convey the image of a peace-loving and internationally modest new Germany. Heinemann died in Essen on 7 July 1976.
Nicholls, Anthony James. The Bonn Republic: West German Democracy, 1945–1990. London and New York: Longman, 1997.; Vinke, Hermann. Gustav Heinemann. Bornheim-Merten: Lamuv-Verlag, 1986.; Webb, Adrian. Germany since 1945. London and New York: Longman, 1998.