Marion is a leading transport and cities expert with a long history in public policy. She has worked on tax policy for the federal Treasury, and led the design and development of the MyGov account. She has provided expert analysis and advice on labour market policy for the Federal Government, the Business Council of Australia, and at the Australian National University.

Marion joined Grattan Institute in 2015 to establish the Transport Program, which she expanded to include Cities in 2016. At Grattan, Marion has published on a wide variety of topics, including investment in transport infrastructure, cost overruns, value capture, traffic congestion, discount rates, and the ways the COVID crisis is changing Australian cities.