"Happy to be back in the capital of hockey," Komarov said on Twitter. "See you soon."
Komarov, 27, played his lone NHL season with the Maple Leafs in 2012-13, when he had four goals and nine points in 42 games.
Last season, he had 12 goals and 34 points in 52 games with Moscow Dynamo of the Kontinental Hockey League. He won a bronze medal with Finland at the 2014 Sochi Olympics, scoring no points with a plus-3 rating in six games.
"Leo offers a lot more than I think that we even got out of him two years ago," Maple Leafs general manager Dave Nonis said. "He's a better player, he's better offensively, he can play with good players, he's done that on the world stage with a pretty good hockey team.
"He's a guy that can play up and down the lineup and it was very important to us that we put a pretty good effort in to get Leo to come back here."