After working as a judge's associate in the Federal Court, with various Aboriginal and other community organisations and in the Commonwealth Parliament’s research service, Sean joined UNSW Law in May 2002. Between 2002 and 2005 Sean was Director of the Treaty Project at the Gilbert + Tobin Centre of Public Law, an ARC-funded project investigating the public law implications of a treaty or treaty-like agreements between Indigenous peoples and Australian governments.
Together with project partners George Williams, Larissa Behrendt and Lisa Strelein, he co-authored the book Treaty (2005). Sean continued his association with the Centre thereafter as the Director of the Indigenous Legal Issues Project and in 2014 he was appointed Centre Director.
He teaches, writes and researches mainly in the areas of constitutional law, native title, land rights and other Indigenous legal issues. He is a co-author of Blackshield and Williams Australian Constitutional Law and Theory – Commentary and Materials (2014) and Indigenous Legal Issues: Commentary and Materials (2009) as well as numerous chapters, journal articles and submissions, mainly dealing with the intersection of public law and Indigenous issues.