[1] At the 1983 election, she won one of the South-East Metropolitan Province seats in the Western Australian Legislative Council.
With Carmen Lawrence's rise to premier in February 1990, a significant reshuffle saw Hallahan become Minister for Planning, Lands, Heritage and the Arts.
At the 1993 election, she moved to the Legislative Assembly, successfully contesting the seat of Armadale and in doing so replacing Bob Pearce whose career had effectively been ended by the WA Inc royal commission.
At the 2004 federal election, following the death of one preselected candidate and the resignation of her replacement, Hallahan nominated to run for Liberal-held Division of Canning, which included Armadale, but was defeated.
However unlike Hallahan, MacTiernan eventually found her way to Federal Parliament when she won the seat of Perth at the 2013 election.