The deal was made with the restricted free agent hours before the Senators’ season opener against the Toronto Maple Leafs.
Tkachuk, 22, has been the Senators’ leading scorer the past two seasons, including 17 goals and 19 assists while playing all 56 games of the 2021 campaign.
“We are delighted to have reached a long-term agreement with Brady,” Senators owner Eugene Melnyk said in a statement. “He is a valued member of our leadership group, he is universally respected by his teammates and a player who we are sure will have a significant impact on our success in the seasons to come.”
Senators general manager Pierre Dorion hailed Tkachuk as a “prototype power forward in today’s NHL.”
The deal binds Tkachuk to the Senators throughout the 2027-2028 season.
Senators choose Tkachuk, son of 1,000-point scorer Keith tkachuk, No. 4 in the 2018 NHL Draft. He was an All-Star in 2020 and has 60 goals and 65 assists in 198 career games.