The team announced the move late Wednesday night after losing 3-2 to the Vancouver Canucks in a shootout. Schmidt's new deal is worth $5.95 million per year.
Schmidt, 27, was suspended 20 games last month for violating the NHL's performance-enhancing drug policy. He can return to the club Nov. 18.
Schmidt led the Western Conference champions in ice time last season at 22:14 per game. He had five goals, 31 assists and 19 penalty minutes in 76 games. He added three goals and four assists with four penalty minutes in 20 playoff games for the expansion Golden Knights, who lost to the Washington Capitals in the Stanley Cup Final.