He was elected to the Ontario legislature in the
1977 provincial election, defeating
Progressive Conservative Don Luckham by 641 votes in the southwestern Ontario riding of
Kent—Elgin. In the
1981 election, he defeated PC challenger Wes Thompson by 337 votes. The Liberal Party made an electoral breakthrough in the
1985 provincial election, and McGuigan was re-elected by a significant margin. Following the election, the Liberals were able to form a
minority government with support from the
Ontario New Democratic Party. During the next five years he was appointed as
parliamentary assistant to several ministers including the Energy, Natural Resources, Transportation and Agriculture. Ontario's electoral map was redistributed before the
1987 election, and McGuigan was forced to face NDP incumbent
Pat Hayes in the new riding of
Essex—Kent. McGuigan won by 1,063 votes, as the Liberal Party won a landslide majority across the province. The NDP defeated the Liberals in the
1990 provincial election, and Hayes defeated McGuigan by almost 6,000 votes. He retired from politics after his defeat. ==After politics==