Crevier, who is in the final season of a two-year contract he signed with the Blackhawks on July 17, 2025, could have become a restricted free agent after the season. He now is signed through the 2030-31 season.
He had offseason shoulder surgery, but is fully recovered.
"I think when you when I've watched him at practice, we've had lots of discussions about him, we watched him in the games, he's moved the puck well, skated well," Sabres coach Lindy Ruff said. "I think there was a little concern coming off of surgery this summer but everything was great and I think he's been a great fit for our hockey club."
Selected by Chicago in the seventh round (No. 188) of the 2020 NHL Draft, Crevier has 32 points (10 goals, 22 assists) in 134 regular-season games.
The Sabres open the regular season at the Columbus Blue Jackets on Thursday (7 p.m. ET; CBJHN, CBJNHL, MSG-B).
NHL.com independent correspondent Craig Merz contributed to this report