David G. Hallman grew up in Waterloo, ON, and studied community psychology at Wilfrid Laurier University and arts and culture at L’Université Paris-Sorbonne. He worked for more than thirty years on the national staff of The United Church of Canada carrying a wide range of social justice responsibilities. Environmental ethics was the major component of his portfolio during his career. In addition to his work in Canada, he also served from 1988 to 2006 as the Co-ordinator of the World Council of Churches Climate Change Programme based in Geneva which involved him in UN global negotiations on climate change. 

In 1993, David was awarded an honorary Doctor of Divinity degree from United Theological College, McGill University, Montreal. In May 2014, he received an honorary Doctor of Divinity degree from Victoria University (University of Toronto).

David is the author and editor of many articles and books on ecological themes including A Place in Creation — Ecological Models in Science, Religion and Economics (UCPH 1992), Ecotheology - Voices from South and North (WCC/Orbis Books 1994 and reissued in 2008),  Spiritual Values for Earth Community (WCC Books 2000 and reissued in 2011) and a major study paper on Climate Change and Poverty — Science, Theology, and Ethics (2005) for the National Religious Partnership on the Environment (USA).

David has lived in Toronto for most of his life. His partner of thirty-three years, William Conklin, died in August 2009 two weeks after being diagnosed with pancreatic cancer. David has written a memoir entitled August Farewell — the last sixteen days of a thirty-three-year romance in which he chronicles the final days of Bill's life interspersed with vignettes from their life together. His first novel, Searching for Gilead, was published in the fall of 2011. Book Tales, a collection of gay literary short stories, came out in September 2016.