The 26-year-old forward could have become a restricted free agent Oct. 9.
Stephenson scored 26 points (11 goals, 15 assists) in 65 games with the Golden Knights and Washington Capitals this season, including 22 points (eight goals, 14 assists) in 41 games after he was traded to Vegas on Dec. 3, 2019. He scored five points (three goals, two assists) in 20 postseason games.
"Chandler was a really good fit upon joining our team," Golden Knights general manager Kelly McCrimmon said. "Great utility in terms of his ability to play throughout the lineup. Real dimension of speed and a player we think is going to be an important part of our team over the next four years."
Selected by Washington in the third round (No. 77) of the 2012 NHL Draft, Stephenson has scored 55 points (22 goals, 33 assists) in 209 regular-season games and 12 points (five goals, seven assists) in 50 Stanley Cup Playoff games.
Stephenson won the Stanley Cup with the Capitals in 2018.
NHL.com independent correspondent Danny Webster contributed to this report
