The 31-year-old forward had 38 points (16 goals, 22 assists) in 56 games last season.
"As you further your career, you understand where you want to play and where your work is, so for me it was pretty simple," Smith said Thursday. "I wanted to play here and negotiate a deal with this team. I feel like I put my heart and soul into this organization. I'm very fortunate they noticed that and have given me the opportunity to chase the goal we started five years ago."
Selected by the Dallas Stars in the third round (No. 69) of the 2009 NHL Draft, Smith has 417 points (174 goals, 243 assists) in 686 regular-season games for the Golden Knights, Florida Panthers, Boston Bruins and Stars, and 65 points (22 goals, 43 assists) in 84 Stanley Cup Playoff games.
"We felt this was extremely important to keep Reilly in our organization," Golden Knights general manager Kelly McCrimmon said Thursday. "He's a Day One Knight. He represents everything we stand for. He's an exceptional two-way player."
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The Golden Knights also signed forward Brett Howden to one-year, $1.5 million contract.
The 24-year-old forward, who became an unrestricted free agent after he did not receive a qualifying offer from Vegas, had 20 points (nine goals, 11 assists) in 47 games last season.
Selected by the Tampa Bay Lightning in the first round (No. 27) of the 2016 NHL Draft, Howden has 69 points (25 goals, 44 assists) in 225 regular-season games for the Golden Knights and New York Rangers, and no points in three playoff games.
NHL.com independent correspondent Paul Delos Santos contributed to this report
