Selected by the Pittsburgh Penguins in the second round (No. 54) of the 2011 NHL Draft, Harrington played two seasons with Wilkes-Barre/Scranton of the American Hockey League and made his debut with the Penguins on Dec. 18, 2014.

Harrington was traded to the Toronto Maple Leafs on July 1, 2015, in a deal that sent Phil Kessel to the Penguins. Harrington had one assist in 15 games with Toronto and was then traded to the Blue Jackets on June 25, 2016. He scored three points in 32 games with Columbus, including his first NHL goal against the Ottawa Senators on Jan. 22, 2017.

Harrington scored 17 points (two goals, 15 assists) in 73 regular-season games for the Blue Jackets in 2018-19, then helped them win a Stanley Cup Playoff series for the first time, a sweep against the Tampa Bay Lightning in the Eastern Conference First Round. He had four assists in 10 playoff games.

Harrington signed a one-year contract with the San Jose Sharks on Sept. 30, 2022. He was in training camp on a professional tryout contract.

NOTES & TRANSACTIONS

• OHL All-Rookie Team (2010)
• OHL First All-Star Team (2012, 2013)
• Traded to Toronto by Pittsburgh with Nick Spaling, Kasperi Kapanen, Pittsburgh's 1st round pick (later traded to Anaheim -- Anaheim selected Sam Steel) in 2016 NHL Draft and New Jersey's 3rd round pick (previously acquired, Toronto selected James Greenway) in 2016 NHL Draft for Phil Kessel, Tyler Biggs, Tim Erixon and Pittsburgh's 2nd round pick (previously acquired, Pittsburgh selected Kasper Bjorkqvist) in 2016 NHL Draft, July 1, 2015.
• Traded to Columbus by Toronto with a conditional pick in 2017 NHL Draft for Kerby Rychel, June 25, 2016.
• Signed as a free agent by San Jose, September 30, 2022.