[5] On July 1, 2015, Harrington was traded to the Toronto Maple Leafs in a multi-player blockbuster deal for Phil Kessel.

[6] Following the trade, Harrington impressed at the Maple Leafs' training camp, making the NHL roster for the opening night of the 2015–16 season.

However, injuries plagued Harrington's season, and he would only play 32 games collectively for the Maple Leafs and their American Hockey League (AHL) affiliate, the Toronto Marlies.

[2] He also helped the Blue Jackets advance past the first round of the postseason for the first time in franchise history by recording four assists through 10 playoffs games.

[18] After attending training camp, Harrington was re-assigned to continue his tryout with the Ducks AHL affiliate, the San Diego Gulls.

As a free agent, Harrington opted to return to North America and signed a one-year AHL contract with the St. Louis Blues primary affiliate, the Springfield Thunderbirds, on July 12, 2024.