Marleau's return should boost the Sharks (0-4-0), who tied the worst start in their history; they also began the 1993-94 season with four straight losses.
"Today was a good day to see Patty and he put some smiles on a lot of faces around here," Sharks forward Logan Couture said. "Obviously losing four in a row, it's not fun here coming to the rink, and you're disappointed in the way you played. Hopefully he adds some energy to our team tomorrow and we play well."
On June 27, Marleau had the final season of his Maple Leafs contract bought out by the Carolina Hurricanes, making him an unrestricted free agent. Carolina acquired Marleau in a trade from Toronto on June 22 with a conditional first-round NHL Draft pick and a seventh-round pick in the 2020 NHL Draft for a sixth-round pick in 2020.
Maple Leafs coach Mike Babcock texted Marleau on Tuesday and said he was happy that he'll remain in the NHL.
"I'm glad it's all worked out for him," Babcock said. "It probably took a little longer than he wanted, but he said last night his wife and kids were real happy. As we all know anybody who has a wife and kids, that's a real important thing. Patty wants to keep playing past this year as well, so we wish him luck."
Selected by San Jose with the No. 2 pick in the 1997 NHL Draft, Marleau has 1,166 points (551 goals, 615 assists) in 1,657 NHL games and 127 points (72 goals, 55 assists) in 191 Stanley Cup Playoff games.
He is the Sharks leader in games played (1,493), goals (508) and points (1,082).
"There's a lot of work to do, a lot to prove again to myself and to everybody who's supported me," Marleau said. "Now is the time to get the work boots on, go out on the ice and help the team."
NHL.com staff writer Tracey Myers and independent correspondent Dave McCarthy contributed