Martindale was born in Brockville, Ontario. He holds a Bachelor of Arts degree from Brock University (1973) and a Master of Divinity degree from Victoria University (1976). He is an ordained United Church minister, and has practiced in Saskatchewan (1976–80) and at a mission in north-end Winnipeg (1980–90). He has been involved in several outreach programs among Winnipeg's poor and aboriginal communities, and remains active in efforts to combat homelessness. He helped to convert St. John's United Church into a co-op apartment complex, and was a founding member of Inner City Voice newspaper. In the legislature, he has served as Chair of the Justice, Social and Economic Development Committees.