 From 1965 to 1967 and again from 1972 to 1981, he was a lecturer at McGill University.He also taught at the Labour College of Canada (now affiliated with Athabasca University) in 1963 to 1965.Hartt recalled in an interview that then Prime Minister Pierre Trudeau suggested in 1978 that Hartt should follow in his father’s footsteps and run as a Liberal but he declined and became a support of the Progressive Conservative Party “after they showed me the books.”

From 1985 to 1988, he was the Deputy Minister in the Department of Finance under Finance Minister Michael Wilson.