While playing in the CFL for the Hamilton Tiger-Cats he intercepted Joe Theismann four times in one game. Brenner also was part of "The Game of the Century", where both Michigan State and Notre Dame were ranked number one in the country and went to a 10–10 tie in 1966.
Brenner was reported missing in April 1983. He, his wife, and four children were residents of Burlington, Ontario. Brenner is featured in a Fifth Estate program on December 3, 2010 which discusses his disappearance and subsequent resurfacing eight years after abandoning his family. He is interviewed living in an unnamed small town in North Carolina and says he cannot explain why he left.