Thomas attended Scotch Plains-Fanwood High School in Scotch Plains, New Jersey during his freshman and sophomore years. For his junior and senior years, he attended Saint Benedict's Preparatory School. He led the school to two Prep A Division New Jersey State titles with a 56–3 record in his final two seasons while averaging 14.5 points and 6.5 rebounds per game his senior year. In 2005, Thomas played at the USA Basketball Youth Development Festival where he helped the Blue Team win the silver medal with a 3–1 record. Following his senior year, he played in the 2006 McDonald's All-American game. Considered a four-star recruit by Rivals.com, Thomas was listed as the No. 13 small forward and the No. 42 player in the nation in 2006. After committing to Duke University on April 5, 2006, Thomas played for the Under 18 national team at the FIBA Americas Under-18 Championship where he helped USA win the gold medal.
College career
Duke (2006–2010)
2006–07 season
As a freshman, Thomas averaged 4.0 points and 2.5 rebounds per game, while shooting.568 from the field, in 31 games.
2007–08 season
As a sophomore, Thomas averaged 4.3 points and 3.3 rebounds in 18.5 minutes in 32 games. He posted a.505 field goal percentage and recorded at least five rebounds 12 times, including eight of Duke's 16 ACC games. Thomas' career high in points came on November 28, 2008, when he scored 21 against Duquesne. His new career high broke his previous record of 15 points set on November 20, 2006. Thomas' ability to finish shots was a big staple of his improvement. It was said of him, "If he gets the ball within three feet of the basket, chances are he's going to put the ball in the hoop — regardless of whether he's fouled."
2008–09 season
As a junior, Thomas averaged 5.3 points and 3.6 rebounds while shooting.626 from the field, in 37 games. Thomas felt that the biggest difference between this year's Duke team and the ones from the last two years, was experience.
2009–10 season: NCAA championship
In his senior year, Thomas and All-American point guard Jon Scheyer were co-captains of Duke's team. In January 2010, Thomas had a career-high 12 rebounds against NC State. On February 10, the eighth-ranked Blue Devils held on for a 64–54 victory against rival North Carolina. However, Thomas suffered a severe bone bruise to his right knee early in the second half, forcing him to miss the next game against Maryland. Thomas helped Duke win the 2010 NCAA championship, their fourth since 1991. In the 2010 NCAA championship game, Duke faced Butler and star swingman Gordon Hayward. The Bulldogs had a chance to win with 3.6 seconds left, but Hayward missed a half-court shot, giving Duke a 61–59 win. Thomas was named to the 2009–10 ACC All-Defensive Team for 2010 and finished his college basketball career ranked 10th on Duke's all-time list in offensive rebounds. In 40 games as a senior, he averaged 4.8 points and 4.9 rebounds in 25.3 minutes per game.
Between November 2010 and December 2011, Thomas played in the NBA Development League for the Austin Toros. On December 9, 2011, Thomas signed with the New Orleans Hornets for training camp. He made the Hornets' roster for the start of the lockout-shortened 2011–12 NBA season, but he was later waived by the team on December 31. On January 4, 2012, Thomas was reacquired by the Austin Toros. He was later selected to play in the 2012 NBA Development League All-Star Game. In 65 games for Austin over two seasons, he averaged 13.4 points, 6.2 rebounds and 1.3 assists per game.
New Orleans Hornets/Pelicans (2012–2013)
On February 6, 2012, Thomas was called up by the New Orleans Hornets, signing a 10-day contract with the team. He later signed a second 10-day contract on February 16, and a multi-year deal on February 27. In 2012–13, Thomas played in 59 games for the Hornets, averaging 2.5 points and 1.9 rebounds per game. In April 2013, the Hornets were renamed the New Orleans Pelicans. On July 10, 2013, Thomas was waived by the Pelicans. He later re-signed with the Pelicans on August 22, but he managed just five games for the team in 2013–14 before be was waived again on November 12. In 106 games for New Orleans over three seasons, he averaged 3.0 points and 2.3 rebounds in 12.4 minutes per game.
On December 27, 2013, Thomas signed with the Foshan Dralions for the rest of the 2013–14 CBA season. In 16 games for Foshan, he averaged 26.1 points, 10.8 rebounds, 1.0 assists and 1.6 steals per game.
On September 29, 2014, Thomas signed with the Oklahoma City Thunder. Thunder head coachScott Brooks said of Thomas, "Lance is a hard worker. He's a player that can guard multiple positions. He gives you everything he has and that's what you want."
On January 5, 2015, Thomas was traded to the New York Knicks in a three-team, six-player trade that also involved the Thunder and the Cleveland Cavaliers. He was waived by the Knicks two days later. On January 10, Thomas returned to the Knicks on a 10-day contract. He later signed a second 10-day contract on January 21, and a rest-of-season deal on January 31. On March 22, 2015, Thomas scored a career-high 24 points in a 106–89 loss to the Toronto Raptors. On July 10, 2015, Thomas re-signed with the Knicks. On December 21, 2015, he tied his career high of 24 points in a 107–99 loss to the Orlando Magic. On July 8, 2016, Thomas again re-signed with the Knicks. Prior to the start of the 2017–18 season, Thomas was named co-captain of the Knicks alongside Courtney Lee. On June 29, 2019, he was waived by the Knicks.
Brooklyn Nets (2020–present)
On September 27, 2019, Thomas signed with the Brooklyn Nets, but was waived on October 18. On July 14, 2020, the Nets signed Thomas as a substitute player.
