The forward, who turns 33 on July 20, had 23 points (nine goals, 14 assists) in 81 regular-season games for the Senators last season and one assist in four Stanley Cup Playoff games.
Cousins, who won the Cup with the Florida Panthers in 2024, could have become an unrestricted free agent at noon ET Wednesday.
“Nick has proven his value to our hockey club over the past two seasons,” Ottawa general manager Steve Staios said. “He brings Stanley Cup winning experience and is an important player inside our dressing room.”
Selected by the Philadelphia Flyers in the third round (No. 68) of the 2011 NHL Draft, Cousins has 218 points (86 goals, 132 assists) in 723 regular-season games for the Philadelphia Flyers, Arizona Coyotes, Montreal Canadiens, Vegas Golden Knights, Nashville Predators, Panthers and Senators and 16 points (four goals, 12 assists) in 72 playoff games.