In 1978 Rau became Minister President of North Rhine-Westphalia, where he remained until 1998, winning four elections for the SPD, which became biggest party in the Landtag each time and gained an absolute majority three times, in 1980, 1985, 1990 and finally 1995. From 1995 onwards, Rau led an SPD-Greens coalition in NRW.