Duclair was acquired in February from Columbus as part of the trade that sent Ryan Dzingel to the Blue Jackets, and he finished with 19 goals and 33 points in 74 games last season.
Only 23, the Senators are Duclair's fifth NHL team, after he was drafted in the third round by the New York Rangers in 2013.
"We are pleased with what Anthony was able to add to our lineup after his acquisition," general manager Pierre Dorion said. "The signing improves our team speed and scoring depth up front. Anthony's speed and skill can be dynamic and at only 23 years old, we feel he has the chance to grow into a really consistent contributor."
The Sens are in full rebuild mode, so Duclair should have a solid opportunity to surpass the 20 goals he scored in his first full NHL season in 2015-16 as a member of the Arizona Coyotes.