The diocese in Joliette says Gravel passed away from lung cancer this morning at the Centre hospitalier regional de Lanaudiere, northeast of Montreal.
The 61-year-old acknowledged not long ago he had smoked for 49 years.
The outspoken social activist represented the Montreal-area riding of Repentigny in the Commons between 2006 and 2008.
Gravel was known for his progressive stands on issue like homosexuality and the role of women in the church.
During his time in Ottawa, Gravel faced attacks from anti-abortion organizations after displaying his support for Dr. Henry Morgentaler when the late physician received the Order of Canada in 2008.
More recently, he was critical of the Parti Quebecois government's now-defunct proposed values charter, describing it in an open letter as "worthy of a dictatorship" in an open letter.
He confirmed last October he'd been diagnosed with stage four lung cancer.
Prime Minister Stephen Harper was among many to weigh in on the death of the popular priest, sending along his condolences through Twitter.
"Laureen & I offer our condolences to the family of Raymond Gravel," the account read. "Raymond was a former colleague of mine from the HoC & will be missed."
A funeral will be held Friday afternoon in Joliette.