He entered the legislative assembly through a 1981 by-election and was re-elected in 1982, 1986, 1989, 1993 and 1996. A Liberal he became minister of health and social services under PremierJoe Ghiz in 1986. He became minister of agriculture in 1989 and minister of education in 1993. In 1996 he became leader of the Liberal Party and was briefly premier of the province before his government's defeat in that year's election.
Having announced he would be seeking the Liberal nomination in the federal riding of Egmont. [1], on November 3, 2007, at the nominating Liberal convention, he lost the nomination to Robert Morrissey[2]. When Morrissey steped down, however, Milligan was acclaimed as the new candidate on September 9, 2008. [3]