He became Secretary of State for the budget and Flemish affairs (1977–1979, Tindemans II & Vanden Boeynants II), Minister of Development Aid (1979–1980, Martens I, Martens II & Martens III) and Minister of Finance (1980–1981, Martens IV). Eyskens became the 45th Prime Minister of Belgium on 6 April 1981, an office his father had held six times. His government quickly collapsed on 17 December, due to disagreements on the financing of the Walloon steel industry. After the fall of his government he served as Minister for Economical Affairs (1981–1985, Martens V) and Minister of Finance (1985–1988, Martens VI & Martens VII). Although originally not a member of the Martens VIII cabinet, on 19 June 1989 he re-entered the government when he replaced Leo Tindemans as Minister of Foreign Affairs (1989–1992, Martens VIII & Martens IX). This was the last government office he held. He served as a backbencher 1992–2003 and retired at the 2003 general election.