The Penguins receive Kessel, Tyler Biggs, Tim Erixon and a 2016 second-round pick, while the Leafs receive Nick Spaling, Kasperi Kapanen, Scott Harrington, a 2016 first-round pick and a 2016 third-round pick.
TSN's Bob McKenzie first reported the trade.
Kessel, who ESPN.com reports was owed a $4 million signing bonus on Wednesday, has been the subject of trade rumors this off-season. The 27-year-old scored 25 goals and tallied 36 assists in 82 games 2014–15, averaging 18:48 time on ice.
Kessel is a three-time All-Star and won the Bill Masterton Memorial Trophy in 2007. He is under contract through the 2021–22 season after signing an eight-year extension with Toronto in 2013.
Kapanen, a winger, was the Penguins' first-round pick at last year's NHL draft. Harrington, a defenseman, was chosen 54th by Pittsburgh in 2011. He appeared in 10 games for the Penguins last season.
- Molly Geary