[4] At the leadership convention, Thornhill was eliminated on the first ballot, finishing third behind Gerald Doucet and John Buchanan.
[5] Thornhill ran in the 1974 election, and defeated Liberal cabinet minister D. Scott MacNutt by 620 votes in the Dartmouth South riding.
[7] On October 5, 1978, Thornhill was appointed to the Executive Council of Nova Scotia as Minister of Development, Chair of the Treasury Board, and Deputy Premier.
[2][8] In June 1979, Premier John Buchanan restructured most government departments,[9] which included Thornhill giving up the Chair of the Treasury Board.
[10] In March 1980, it became public knowledge that in 1977 and 1978, Thornhill, who had personal financial problems negotiated with four banks for forgiveness of a series of loans he had made years earlier, some of this occurring while he was serving as Chair of the Treasury Board.
[11] Thornhill was re-elected in the 1981 election,[12] and remained as Minister of Development when Buchanan shuffled his cabinet in December 1981.