Leddy was selected by the Minnesota Wild in the first round (No. 16) of the 2009 NHL Draft, and was traded to the Chicago Blackhawks on Feb. 12, 2010.

Following his junior year at Eden Prairie High School in Minnesota, Leddy was invited to join the USA Hockey National Team Development Program. Instead, he returned to high school for his senior year, helped Eden Prairie to a state Class 2A championship title and was named Mr. Hockey for the state of Minnesota following a 12-goal, 45-point season.

He remained home for college, attending the University of Minnesota, where he scored three goals and 11 points in 30 games in 2009-10 and was named the Golden Gophers rookie of the year.

Leddy signed a three-year contract with the Blackhawks and made his NHL debut against the Colorado Avalanche on Oct. 7, 2010. He scored his first NHL goal two games later against the Buffalo Sabres. He was sent to Rockford of the American Hockey League on Oct. 17 and helped the United States finish third at the 2011 IIHF World Junior Championship. Leddy was recalled by Chicago on Jan. 7, 2011 and ended the season with four goals and seven points in 46 games.

By 2011-12, Leddy was an established defenseman and played all 82 games for the Blackhawks, finishing with 34 assists and 37 points. During the 48-game shortened season of 2012-13, he scored six goals during the regular season and helped the Blackhawks to their second Stanley Cup championship in four seasons.

Following the 2013-14 season, when Leddy scored seven goals and 31 points in 82 games, he was traded to the Islanders on Oct. 4, 2014. He immediately stepped into a top-four role, averaging 20:22 of ice time in his first season and leading their defensemen with 10 goals, 37 points and plus-18.

The Islanders signed Leddy to a seven-year contract Feb. 24, 2015. His ice time jumped to 22:37 per game for the 2015-16 season, when he scored five goals and 35 assists. In helping the Islanders reach consecutive Stanley Cup Playoff appearances for the first time since the 2003-04 season, Leddy averaged 27:04 of ice time in the 2016 postseason, scoring a goal and four points to help New York advance to the second round for the first time since 1993.

After Leddy was minus-42 in 2017-18, he responded with an even rating the following season to help the Islanders again reach the second round of the playoffs. He then played for the Detroit Red Wings and St. Louis Blues, and signed a four-year, $16 million contract to remain with the Blues on July 13, 2022.

NOTES & TRANSACTIONS

• Traded to Chicago by Minnesota with Kim Johnsson for Cam Barker, February 12, 2010.
• Traded to NY Islanders by Chicago with Kent Simpson for T.J. Brennan, Ville Pokka and Anders Nilsson, October 4, 2014.
• Traded to Detroit by NY Islanders for Richard Panik and a 2nd-round pick in 2021 NHL Draft, July 16, 2021.
• Traded to St. Louis by Detroit with Luke Witkowski for Jake Walman, Oskar Sundqvist and a 2nd-round pick in the 2023 NHL Draft, March 21, 2022.