Allen's career began with history and he specialized in Christian socialism within Canada. In 1971, he published a work entitled The Social Passion, chronicling the history of the Canadian social gospel from the 1890s to 1929. In the book he proposed that the social gospel supplied the reform movement with a type of ideology. He said it ultimately failed because the concept translated poorly between English and Canadian society and that the structure of the churches did not lend itself to promoting social change. The book was criticized because it focused too strongly on central Canada and ignored trends in the Maritimes and Western Canada. In addition to The Social Passion, Allen has published Region of the Mind: Interpreting the Western Canadian Plains, Religion and society in the prairie west and Man and Nature on the Prairie, and was the editor of a collection entitled The Social Gospel in Canada. In 1998 he published a family history, "Sun Bright and Well Beloved: Three Hundred Years of a North American Family and their Farther Past," hailed in the Canadian Historical Review as setting a new standard for family history in Canada. He has also written several articles on Salem Bland, a prominent Canadian Christian socialist. In 2008 Allen published volume one of his biography of Salem Bland, The View from Murney Tower: Salem Bland, the Late Victorian Controversies, and the Search for a New Christianity.
Region of the Mind: Interpreting the Western Canadian Plains, 1973
Religion and society in the prairie west, 1975
Man and Nature on the Prairie, 1976
The Social Gospel in Canada, 1975
Sun Bright and Well Beloved: Three Hundred Years of a North American Family and their Farther Past, 1998
The View from Murney Tower: Salem Bland, the Late Victorian Controversies, and the Search for a New Christianity, 2008
Politics
Allen was elected to the Ontario legislature in a by-election held on June 17, 1982, defeating Liberal Joe Barbara and replacing former Liberal leaderStuart Smith as the Member of Provincial Parliament for Hamilton West. He was re-elected over Liberal Paul Hanover by 450 votes in the 1985 provincial election, and defeated Liberal Mary Kiss by 1,096 votes in the provincial election of 1987. In 1983, Allen introduced a resolution calling for Ontario to be made a nuclear-free zone. It was defeated by a vote of 63 to 38. As the NDP critic for Constitutional Affairs and a member of l'Association interparlementaire de langue francaise, Allen was a vocal supporter of the Meech Lake Accord, and with Liberal critic, Charles Beer, drafted the Ontario Legislature's official report on the Accord.