The federal Liberal leader and his wife, Sophie Gregoire-Trudeau, are expecting their third child.
The couple already have two youngsters: Xavier, 6, and Ella-Grace, 4.
The new baby is due in March.
Trudeau spokeswoman Mylene Dupere says the leader's staff was told the happy news on Monday.
Trudeau, meanwhile, has taken to Twitter to let the rest of the world in on the big news.
"Thrilled to let you know we're going to need another seat in our canoe: Sophie is pregnant!" he tweeted, posting a photo of the couple and their two kids paddling a canoe.