Buffalo drafted Samuelsson with the 32nd pick in 2018. He recently completed his sophomore season at Western Michigan University, where he tallied two goals and 14 points in 30 games.
He was an All-NCHC honorable mention this season and a finalist for the conference's Defensive Defenseman of the Year award.
"We are very pleased with Mattias' growth both at Western Michigan and on the international stage," Sabres general manager Jason Botterill said. "He possesses a unique combination of size, speed, and skill, and we look forward to working with him on his next steps as a pro."
Samuelsson, 20, has represented the United States at the IIHF World Junior Championship the past two years. He earned a silver medal in 2019 and served as captain in 2020.