Financial terms of the contract were not disclosed but several reports said Myers, who won the Calder Trophy as rookie of the year for the 2009-10 NHL season, will earn $38.5 million over the length of the deal.
Myers, who shared the team lead with five game-winning goals last season, still has one year remaining on the entry level contract he signed in 2009.
"I am very grateful that (general manager Darcy Regier) and the Sabres initiated discussions one year early, and showed the confidence in making it a long term deal," Myers, 21, said in a report on the team's website.
"It's what I wanted ever since I came in two years ago, I've wanted to be a Sabre for a long time. I'm very excited today to solidify a long term spot, and to be a part of this organization as it grows."
Myers, who was selected 12th overall by the Sabres in the 2008 NHL Entry Draft, had 10 goals and 27 assists last season and led all Buffalo defenseman with 37 points.
(Reporting by Frank Pingue in Toronto; Editing by Mark Lamport-Stokes)