McHattie was born in Antigonish, Nova Scotia. A graduate of American Academy of Dramatic Arts, he has appeared in many films and television shows including Star Trek: Deep Space Nine, Star Trek: Enterprise, Highlander: The Series, and American Playhouse's Life Under Water (1989). His roles include 300, A History of Violence, The Fountain, Secretary, Shoot 'Em Up, Life with Billy, One Dead Indian, Beverly Hills Cop III. He also appeared in Canada: A People's History as Major-General Sir Isaac Brock, and in The Rocket as legendary coach Dick Irvin. He also portrayed Jacques Pasquinel in the James A. Michener production of Centennial. He portrayed an extraordinary USMC sniper in the JAG season one episode "High Ground".

In 1976 McHattie played James Dean in the television movie James Dean: Portrait of a Friend. A television adaptation of the Biography written by James Dean's friend and writer Bill Bast.

McHattie also appeared in several episodes of Seinfeld (beginning with "The Wallet") where he played Dr. Reston, Elaine Benes' manipulative psychiatrist/boyfriend. He also appeared in two episodes of The X-Files. McHattie recently appeared in the pilot of Sabbatical, voiced the villain The Shade in Justice League, and portrayed Hollis Mason, the first Nite Owl, in the film adaptation of Watchmen.

In 2009, McHattie appeared in the American thiller Summer's Blood as Gant Hoxey, alongside Twilight actress Ashley Greene, who portrays Summer. He is set to co-star Felicia Day and Kavan Smith in the gothic adaption of Red Hiding Hood, called Red.

He is married to actress Lisa Houle, with whom he has three children. He was previously married to Meg Foster.