He taught geology at St. Francis Xavier University in Antigonish, Nova Scotia from 1967 to 1970.
[2][6] Gillis first attempted to enter provincial politics in the 1967 election, but lost to Progressive Conservative William F. MacKinnon by 26 votes.
[7][8] He ran again in the 1970 election and defeated Progressive Conservative William Shaw by 408 votes to win the Antigonish riding.
[4] Gillis was re-elected in the 1978 election,[14] but the Liberals were defeated[15] and he moved to the opposition benches for the next 15 years.
[18] In the 1993 election, the Liberals led by John Savage won a majority government,[19] and Gillis was re-elected in his riding by over 4,000 votes.