He was diagnosed in February, after having represented the riding as a member of the NDP from 2006 to 2015.
Dewar, 55, has been diagnosed with grade 4 glioblastoma -- the same type of aggressive, incurable brain cancer that claimed the life of Tragically Hip frontman, Gord Downie.
The longtime politician said after losing his seat in the house of commons, he had planned to run for mayor in Ottawa, but his cancer diagnosis took away that possibility.
Now, the focus for Dewar has turned to family. He has two children with his wife of 25 years, aged 22 and 19.
He'll also be launching a new initiative called Youth Action Now at the National Arts Centre June 19, which has a goal of raising money to support grassroots change driven by young people.