"It's very special," Karlsson said. "Being nominated is one thing, but to win it, it's been a crazy year."
The 25-year-old forward finished third in the NHL with 43 goals and led the League with a plus-49 rating in 82 games. He took six minor penalties; his 12 penalty minutes were the fewest among the NHL's top 40 scorers.
Karlsson became the first player to win an end-of-season trophy for a team in its inaugural NHL season since Wayne Gretzky won the Hart and Lady Byng trophies for the Edmonton Oilers in 1979-80.
"I never would have thought a year ago that Vegas would be a hockey town," Karlsson said. "It's crazy to see that, from month to month, it's been growing. They've seemed to really embrace us and it's a fun place to play."
Karlsson, who had 50 points (18 goals, 32 assists) in 183 NHL games prior to this season, had 78 points to help the expansion Golden Knights to the Pacific Division title, the Stanley Cup Final, and records for wins (51) and points (109) by an NHL team in its inaugural season.
"[I'm] going into the summer motivated," Karlsson said. "I want to try and get better. Obviously, we didn't go all the way this year. That's the goal we have. I'm very hungry to get going and excited for next year."
Five players have scored more goals playing for a team in its inaugural season, and seven have had more points.
Buffalo Sabres center Ryan O'Reilly, 27, and Florida Panthers center Aleksander Barkov, 23, were the other finalists. O'Reilly took one minor penalty in 81 games. Barkov had 14 penalty minutes in 79 games.
Here is the voting by the Professional Hockey Writers Association:
Pts. (1st-2nd-3rd-4th-5th)
- William Karlsson, VGK 915 (57-32-15-12-10)
- Ryan O'Reilly, BUF 654 (38-11-23-23-13)
- Aleksander Barkov, FLA 493 (10-30-29-8-14)
- Anze Kopitar, LAK 471 (13-31-15-12-13)
- Jared Spurgeon, MIN 202 (6-8-10-10-6)
- Marc-Edouard Vlasic, SJS 182 (7-5-8-10-7)
- Alex DeBrincat, CHI 169 (3-9-6-11-13)
- Auston Matthews, TOR 157 (6-3-6-14-4)
- Claude Giroux, PHI 123 (6-4-3-4-8)
- Connor McDavid, EDM 119 (2-7-7-4-3)