He is currently playing for the Montreal Canadiens of the National Hockey League (National Hockey League). Lessio was selected 56th overall by the Phoenix Coyotes in the 2011 National Hockey League Entry Draft. Lessio played his final season of major junior hockey with the 2012-2013 Oshawa Generals, scoring 19 goals and 34 points in 35 Ontario Hockey League games.
He also appeared in five American Hockey League games with the Portland Pirates near the end of the 2012-2013 AHL season, where he registered a goal and an assistant
Following a successful pre-season training camp, Lessio made the cut to start the 2013-2014 season in the National Hockey League with the Phoenix Coyotes. In the 2015-2016 season, Lessio was assigned to begin the year with new AHL affiliate, the Springfield Falcons.
On December 15, 2015, Lessio was traded to the Montreal Canadiens in exchange for Christian Thomas. He remained in the AHL, assigned to the Canadiens" affiliate, the Saint John"s IceCaps.
On January 31, 2016, he was called up from Saint John"s to the Montreal Canadiens.