The 2012–13 Oklahoma City Thunder season was the 5th season of the franchise in Oklahoma City and the 47th in the National Basketball Association (NBA). After their trip to the NBA Finals, despite losing the Finals to the Miami Heat in five games, the Thunder improved on last season's output, winning 60 games, earning them the top seed in the Western Conference and second overall. The first round pitted the Thunder against the eight-seeded Houston Rockets, led by James Harden, a former Thunder player. Despite a season-ending injury to Russell Westbrook in Game 2, the Thunder still managed to breeze past the Rockets in six games, to advance to the next round, where they faced the Memphis Grizzlies. The absence of Westbrook, however, affected the Thunder and they would end up losing to the Grizzlies in five games.
 The Thunder finished the 2011–12 season 47–19 in the lockout shortened season to finish in first place in the Northwest Division, second in the Western Conference and qualified for the playoffs. The Thunder made it to the 2012 NBA Finals but were defeated 4–1 against the Miami Heat. Last season featured Kevin Durant's third consecutive scoring title, Durant being named the MVP of the 2012 NBA All-Star Game, All-Star appearances for Durant and Russell Westbrook, James Harden being awarded the NBA Sixth Man of the Year Award and an All-Defensive First-Team selection for Serge Ibaka.
 The Thunder had only their own first-round pick entering the draft. The Thunder traded their 2012 second-round pick in the Robert Vaden trade to the Minnesota Timberwolves back in 2011. The Thunder ended 2012 NBA draft night with Baylor forward Perry Jones.
 
On October 27, the Thunder traded reigning sixth man of the year James Harden, Cole Aldrich, Daequan Cook and Lazar Hayward to the Houston Rockets in exchange for Kevin Martin, Jeremy Lamb, a 2013 first-round pick, a 2013 second-round pick and a 2014 first-round pick. Harden was set to hit restricted free agency following the 2012-13 season and was unable to work out an extension. The Thunder offered a four-year, $55 million extension which was $4.5 million less than the max contract that Harden coveted. Due to the NBA's luxury tax, the Thunder were unwilling to offer a max extension to Harden in order to avoid paying hefty taxes.  We wanted to sign James to an extension, but at the end of the day, these situations have to work for all those involved. Our ownership group again showed their commitment to the organization with several significant offers. We were unable to reach a mutual agreement, and therefore executed a trade that capitalized on the opportunity to bring in a player of Kevin's caliber, a young talent like Jeremy and draft picks, which will be important to our organizational goal of a sustainable team. We appreciate James, Cole, Daequan and Lazar’s contributions to the Thunder organization and this community and wish them the best in the future. Two years later, Harden reiterated the point that he would still be with the Thunder had money not been an issue.
 I felt like I already made a sacrifice coming off the bench and doing whatever it takes to help the team, and they weren’t willing to help me, In exchange for Harden, the Thunder received Kevin Martin and Jeremy Lamb. Martin came off the 2011-12 season as the leading scorer for the Rockets, averaging 17.1 points. Martin, who since been a starter since 2006, became the Thunder's new sixth man. Lamb, a rookie out of UConn was also sent to the Thunder. Lamb was originally selected 12th overall in the 2012 NBA draft coming off two seasons with the Huskies with career averages of 14.1 points.
 For this offseason, free agency began on July 1, 2012, while the July moratorium ended on July 11. Derek Fisher, Royal Ivey and Nazr Mohammed were set to hit unrestricted free agency. On July 27, Royal Ivey and Nazr Mohammed signed with the Philadelphia 76ers and the Chicago Bulls respectively. On November 28, Derek Fisher signed a one-year deal with the Dallas Mavericks.
 On July 11, Hasheem Thabeet signed a contract with the Thunder. Thabeet was originally selected 2nd overall in the 2009 NBA draft that saw James Harden go 3rd overall. Thabeet spent the 2011-12 season with the Houston Rockets and Portland Trail Blazers. On September 12, DeAndre Liggins signed a contract with the Thunder. Liggins was originally selected 53rd overall in the 2011 NBA draft spending only one season with the Orlando Magic last year. On October 31, Daniel Orton signed a contract with the Thunder. Orton, who also spent last season with the Orlando Magic, was originally selected 29th overall in the 2010 NBA draft.
 On August 18, Serge Ibaka agreed to a four-year, $48 million contract extension to stay with the Thunder.
 On October 12, the Thunder announced Mike Wilks as a pro scout. Wilks joins the Thunder after playing seven seasons in the league, including a stint with the Thunder during the 2008-09 season.
 Roster  Last transaction: April 20, 2013
  
 After all games.
‡ Waived during the season
† Traded during the season
≠ Acquired during the season
 After all games.
  
 Via draft
 Via trade
 Via free agency
 Via trade
 Via free agency