Coach Mike Sullivan also rejoined the Penguins on Sunday after exiting COVID-19 protocol.
The Penguins activated Crosby, as well as defensemen Brian Dumoulin, Marcus Pettersson and Chad Ruhwedel. Pettersson and Ruhwedel actually exited COVID-19 protocol earlier this week and played in a game against Florida on Thursday, but they were unable to join the Penguins in Ottawa for Saturday night's game because of Canada's COVID-19 quarantine protocols.
Crosby and Dumoulin went into the protocol on Nov. 3. Sullivan joined them soon after that, part of an outbreak in which eight Penguins and their coach missed time.
Both Crosby and Dumoulin played in Sunday's loss. Crosby went without a point in 16:57 of ice time. It was only his second game of the season; he also missed the first seven games following offseason surgery.
"It's his second game in five months, six months, so I think we have to understand where he's at," said Sullivan after the game. "He's coming off a difficult 10 days that he just went through. I thought he played hard tonight under real challenging circumstances.''
Information from the Associated Press contributed to this report.