Lars Bender played from 1893 to 1999 in the youth of the TSV Brann castle, from 1999 to 2002 he was part of SpVgg Unterhaching youth teams. In summer 2002, he moved to the 1860 München youth team.
In August 2006, he played his first game for 1860 München II in the Regionalliga Süd. In October, he was unused substitute in the 1860 München senior team, and on 27 November 2006, when he was 17 years old, he made his professional debut at the home game against the TuS Koblenz in the 2. Bundesliga. In his first professional season he played 13 matches, nine of them in the starting lineup. In this season, Bender won the Fritz-Walter trophy, ahead of then Mönchengladbach's Marko Marin and his twin brother, Sven Bender. In his second season he was a regular player in the defensive midfield. On the first day of the new season, he scored his first goal. Bender started 2008–09 season again as a regular player. In the second league game against FSV Frankfurt on 3 October 2008, he took over the captaincy and was at 19 the youngest captain in the history of the 1860 München, but on 20 October he was seriously injured and after number of injuries, he finished that season with only 15 matches played. In his three professional seasons played for 1860 München in the 2. Bundesliga, he played 58 games and scored four goals.
On 18 August 2009, Bender signed a three-year contract with Bayer Leverkusen. He played his first match in the Bundesliga coming off the bench on Matchday 6 and was used as substitute in most of 20 games he played during his first season in Bayer Leverkusen. He scored his first goal in the Bundesliga against Eintracht Frankfurt on 16 September, an eventual 4–0 win. In the following season, his position in the defensive midfield remained competitive and he was often second choice, but he played 27 matches and scored three goals. In the 2011–12 season, he was a regular player and played most of the games over the full season, only interrupted by a forced break for a muscle bundle crack injury in the spring of 2012. On 21 March 2012, Bender signed a new contract with Leverkusen to 2018. In the 2012–13 Bundesliga season, he played 33 games, scored 3 goals and made 6 assists. On 31 October 2013, he extended contract with Leverkusen until 2019. In the 2013–14 season, he played 29 games and scored three goals in the Bundesliga, despite being injured for the most of September and October and again in the spring of 2014.
Bender was chosen as part of Germany's 23-man squad for Euro 2012. He scored an 80th-minute winner in the final group game against Denmark.
On 29 May 2013 Bender scored twice in a 4–2 win over Ecuador.
He was named in Germany's provisional 30-man squad for the 2014 FIFA World Cup, but withdrew on 23 May following a thigh injury in training. Manager Joachim Löw said "I feel personally very sorry for Lars because I know how much he wanted to be in Brazil, when a player is ruled out so close before a tournament then it is very disappointing for everyone".