Dr Gallop joined the Australian Labor Party in 1971 where he found a natural home for his opposition to the Vietnam War and support for the reform of Australian society. By 1972 he was President of the University of WA branch and was elected to the WA Legislative Assembly for the seat of Victoria Park in 1986.

From 1990 to 1993, Dr Gallop held Education, Parliamentary and Electoral Reform, Fuel and Energy, and Micro-Economic Reform portfolios in the Lawrence Government, and was Minister assisting the Treasurer. When the Lawrence Government was defeated at the 1993 state elections Dr Gallop was elected Deputy Leader of the State Parliamentary Labor Party.

Dr Gallop was elected Leader of the Opposition in October 1996 and on 10 February 2001, led the Australian Labor Party into government in Western Australia, becoming Premier and Minister for Public Sector Management, Federal Affairs, Science, Citizenship and Multicultural Interests. The Gallop Government won a further term of office on 26 February 2005.

Among the many significant achievements of his Government, Dr Gallop cites saving old growth forests, improving the wellbeing of indigenous Australians and constructing the Mandurah Rail line as some of the things that give him most satisfaction.

On 16 January 2006 Dr Gallop announced his resignation from State Parliament and in July 2006 Dr Gallop took up the position of Professor and Director of the Graduate School of Government at Sydney University.

Professor Gallop graduated with an economics degree at the University of Western Australia and was awarded a Rhodes Scholarship to study at Oxford University.  He studied Philosophy, Politics, and Economics and was awarded a Master of Arts from Oxford in 1974 and later a Doctor of Philosophy from Oxford in 1983. In between these two periods at Oxford, Dr Gallop also completed a Master of Philosophy at Murdoch University in Perth.