A gifted student Dr Gallop completed his undergraduate degree at UWA and his Master of Philosophy at Murdoch, before heading to Oxford University as a Rhodes Scholar.

By 1983, Dr Gallop had published numerous academic articles and lectured in social and political theory at Murdoch and UWA. Dr Gallop's political career began with his election to the WA Legislative Assembly in 1986, representing the seat of Victoria Park. A member of the Australian Labor Party (ALP), he quickly ascended the ranks, holding various shadow ministerial portfolios. In 1996, he was elected leader of the WA Labor Party, positioning him as Leader of the Opposition.

In the 2001 state election, Dr Gallop led the ALP to victory, ending the eight-year tenure of the Liberal-National Coalition government. As Premier, Dr Gallop's administration focused on social reform, economic development, and environmental sustainability. His government introduced significant policies, including labor market reforms, educational initiatives, and healthcare improvements. Notably, Dr Gallop championed the redevelopment of Perth's urban landscape and infrastructure, enhancing the city's functionality and draw as a tourist destination.

Dr Gallop's tenure also saw the introduction of the ‘Gallop Government's Drug Summit’, which aimed to address WA's drug issues through comprehensive community consultation and policy recommendations. Additionally, his government implemented measures to protect WA’s unique environment, such as the creation of new marine parks and conservation areas.

In 2005, Dr Gallop led the ALP to a second electoral victory, reinforcing his government's mandate. However, his tenure was cut short when he resigned in January 2006 due to a diagnosis of clinical depression. His decision to step down and publicly discuss his mental health struggles was widely praised for raising awareness and helping to reduce the stigma surrounding mental illness.

After retiring from politics, Dr Gallop took up a position as Director of the Graduate School of Government at Sydney University from 2006 to 2015. He has been supportive of a range of civil society institutions seeking a better society, most notably the Global Commission on Drug Policy and the New Democracy Foundation. He is now a Emeritus Professor at Sydney University.