Lehner's career took an incredible turn after he signed a one-year contract with the New York Islanders on July 4, 2018.

Before the 2018-19 season, Lehner wrote about his mental health issues and alcoholism during his time with the Buffalo Sabres, and the treatment that helped him recover. He went on to have the best season of his NHL career (25-13-5, 2.13 goals-against average, .930 save percentage), helping the Islanders return to the Stanley Cup Playoffs and allow the fewest goals in the NHL. He won the Masterton Trophy, given for perseverance and dedication to hockey, and was a finalist for the Vezina Trophy as the NHL's top goalie.

However, the Islanders opted not to re-sign Lehner, and he signed a one-year contract with the Chicago Blackhawks on July 1, 2019. He was 16-10-5 for the Blackhawks with a .918 save percentage despite a 3.01 GAA before being traded to the Vegas Golden Knights on Feb. 24, 2020.

Lehner didn't strap on goalie pads until age 10, but by the time he was 15 he was stopping pucks for Sweden's Under-16 team as well as for Frolunda in the Swedish Elite League's under-18 division. He won a league championship with Frolunda's Under-20 team in 2007-08, and in 2008-09 played for Sweden at the IIHF Under-18 World Championship.

The Ottawa Senators selected Lehner in the second round (No. 46) of the 2009 NHL Draft, and Lehner headed to North America to play for Sault Ste. Marie of the Ontario Hockey League in 2009-10. He also made his professional debut that season, starting two games for Binghamton of the American Hockey League and winning both.

Lehner made his NHL debut Oct. 16, 2010, playing the opening 4:42 of the third period of a 4-3 loss to the Montreal Canadiens, stopping all three shots he faced. When he got the start Jan. 13, 2011, against the Islanders, Lehner became the youngest goalie in Senators history at 19 years, 173 days. He stopped 20 shots in a 6-4 win, his first NHL victory.

He continued to split time between Ottawa and Binghamton through 2012-13. In 2010-11 he helped Binghamton win the Calder Cup, going 14-1 with a 2.10 goals-against average and a .939 save percentage in the postseason and winning the Jack A. Butterfield Trophy as the AHL playoff MVP.

On Feb. 28, 2012, Lehner made 32 saves for his first NHL shutout, a 1-0 win against the Boston Bruins. On Feb. 4, 2014, he became the first goalie in Senators history to face 50 shots in a game and earn a victory, making 46 saves on 50 shots in a 5-4 shootout win against the St. Louis Blues.

On June 26, 2015, Ottawa traded Lehner and center David Legwand to the Sabres for the No. 21 pick in the 2015 NHL Draft.

NOTES & TRANSACTIONS

• Jack A. Butterfield Trophy (AHL - Playoff MVP) (2011)
• Traded to Buffalo by Ottawa with David Legwand for NY Islanders' 1st round pick (previously acquired, Ottawa selected Colin White) in 2015 NHL Draft, June 26, 2015.
• Signed as a free agent by NY Islanders, July 4, 2018.
• Signed as a free agent by Chicago, July 1, 2019.
• Traded to Toronto by Chicago for Martins Dzierkals, February 24, 2020.
• Traded to Vegas by Toronto for Vegas' 5th-round pick in 2020 NHL Draft, February 24, 2020.