Gray was born Robert Bruce Gray in San Juan, Puerto Rico to Canadian parents. He was raised on the island until the age of ten when, in 1946, his parents relocated to Saginaw, Michigan then in 1950 relocated again to Toronto, Canada.

He is probably best known to Canadian audiences for his portrayal of investment banker Adam Cunningham on the Global series Traders, the father of the groom in My Big Fat Greek Wedding, and the recurring role of Judge J.E. Reilly on the soap opera Passions.

However, he has made appearances in American media; particularly in science fiction. He portrayed Sky Marshall Dienes in the movie version of Starship Troopers, an interrogator of Captain John Sheridan on Babylon 5, legendary Vulcan philosopher Surak on Star Trek Enterprise and Supreme Court Justice Anthony Kennedy in the 2008 film Recount.

He appeared several times on Star Trek: The Next Generation and Star Trek: Deep Space Nine as Admiral Chekote (contrary to rumor, this character is not related to Chakotay from Star Trek: Voyager). He also had a guest-starring role on the popular cable television series Queer as Folk, playing wealthy gay millionaire George Schickel.

Gray was also the face of the leader of a fictitious anti-Amsterdam organization in a print and internet advertising campaign for Amstel beer.

He is currently seen in a recurring role on Medium, as Joe Dubois' dead father, appearing in dream sequences.