He was selected second overall by the Kings in the 2008 NHL Entry Draft from the Guelph Storm of the OHL, where he was twice voted the league's top offensive defenceman.

He is a two-time Stanley Cup champion with the Kings in 2012 and 2014, two-time Olympic gold medallist with the Canadian national team at Vancouver 2010 and Sochi 2014, 2009 World Championship silver medallist, 2008 World Junior Championship gold medalist, and a Norris Trophy finalist in 2010, 2015, 2016 and 2018, winning the trophy in 2016.

Nonetheless, Doughty felt that his time playing goal in soccer helped him develop an awareness of the players and the game in hockey.

[22] Doughty missed the majority of Los Angeles' training camp as a holdout, including five pre-season games, before signing the contract.

On December 15, Doughty recorded his 100th career assist on a goal by captain Dustin Brown in a 2–1 win over the Columbus Blue Jackets.

[25] Doughty was elevated into a role where he was expected to shut down the opposition's top forwards, forcing him to focus more on his defensive play than his offensive.

Consequently, Doughty's 36 points (10 goals, 26 assists) on the season was his lowest total in three years and the Kings would narrowly qualify for the 2012 playoffs as the eighth and final seed in the Western Conference.

He ended the playoffs was the top-scoring defenceman after recording four goals and 12 assists for 16 points in all 20 games to help the Kings win their first Stanley Cup championship in franchise history.

In doing so, Doughty (along with teammate Jeff Carter) became the seventh and eighth players in league history to win both an Olympic hockey gold medal and the Stanley Cup in the same year.

[34] During the 2015–16 season, Doughty had a career-high plus 24 rating, while also leading the league in shot attempts and ranking third in average ice time for the Kings and played in all 82 games with 51 points (14 goals, 37 assists).

[36] During the 2016–17 season Doughty was selected to participate in the 2017 NHL All-Star Game (along with teammate Jeff Carter) after leading the team's defence in goals and coming in second in points.

On October 8, 2019, Doughty scored the winning goal in a game against the Calgary Flames, but it was his post-goal celebration that received media attention.

Doughty allegedly yelled an expletive at Flames' fans at ice level, while performing a "crotch chop" motion made famous in professional wrestling circles.

[42] After starting the 2021–22 season with seven points leading all NHL defencemen in scoring, on October 22, 2021, Doughty collided knee-to-knee with Dallas Stars defenceman Jani Hakanpää, suffering a tibial plateau contusion.

[44] He would also record three assists but was goalless in the Kings first round exit in the 2023 playoffs by the Edmonton Oilers for the second straight season, this time in six games.

On October 21, 2023, in a 4–2 win over the Boston Bruins, Doughty played his 1,100th NHL game, becoming the fourth player in Kings history to hit the mark with the club.

[60] His strong play in the World Championships earned Doughty an invitation to Canada's summer orientation camp for the 2010 Winter Olympics.

[61] Doughty earned one of the final spots on the Canadian defence, beating out established players such as Dion Phaneuf, Jay Bouwmeester and Mike Green.

[61] He emerged as one of the top defenders on the team,[63] and won the gold medal as Canada defeated the United States in the final game.