Sewell served as chair of the Toronto public housing authority from 1986 to 1988 and is an acknowledged urban affairs expert. He has served as chair of the Royal Commission on Planning and Development Reform in Ontario from 1991 to 1993. Sewell was an advisor to East London, South Africa's city council from 1994 to 1999 and as advisor on the re-establishment of local government in Malawi in 2000. Sewell also taught law, politics and social science at York University from 1989 to 1991.