 He was elected to the Ontario legislature in the 1985 provincial election, defeating New Democratic Party candidate Mike Foster by over 3,000 votes in the Yorkview constituency.He was re-elected by a greater margin in the 1987 election, despite an unusual challenge from Tony Marzilli who ran as an Independent "Trudeau Liberal".Polsinelli was a backbench supporter of David Peterson's government during his time in the legislature, and served as a parliamentary assistant to four different ministers between 1985 and 1990.