Professor Mostert is an Emeritus Professor of the University of Divinity (Melbourne) and was a minister of the Presbyterian Church of Australia and then the Uniting Church in Australia for almost 50 years. He was engaged in parish ministry in Tasmania, missionary service in South Korea, and theological and ministerial education in Sydney (9 years) and Melbourne (17 years). He was a member of both denominational and ecumenical National Commissions. His work has been published in books and journals and he continues his teaching, research and writing, though officially retired in December 2012. He was ordained an Anglican priest in 2016.