Lars van der Haar was born on July 23, 1991, in Woudenberg, the Netherlands. Initially, he practiced gymnastics and judo, but at age eleven, he decided to try his luck on a bike. He first focused primarily on road cycling, but soon discovered that he was more suited to cyclo-cross. In 2009, he achieved his first major success by becoming the Dutch junior champion. In 2010, Van der Haar moved up to the U23 category, where he became European champion in his first year. He went on to win the U23 Cyclo-cross World Championships in both 2011 and 2012.
Starting in 2011, Van der Haar began competing in professional races. In his first year among the elite, he achieved two victories, winning in Las Vegas and Harderwijk. At the time, he rode for the AA Drink Cycling Team.
During the 2012/2013 winter season, Van der Haar had his true breakthrough. In the first World Cup race in Tábor, he finished second. Later that season, he defeated six-time Dutch champion Lars Boom to claim his first national title. Van der Haar capped off his season by taking bronze at the Cyclo-cross World Championships in Louisville.
In the 2013/2014 season, he continued his strong form, winning his first World Cups in Valkenburg, Tábor and Heusden. These victories earned him the overall World Cup title. That year, he also defended his national title, making it his most successful season to date.
During his successful year, Van der Haar rode for the Rabobank Development Team. On March 1, 2014, he made the switch to the Giant-Shimano Development Team. This year proved to be another good one for the Dutchman, with five wins, including World Cup victories in Valkenburg and Heusden. However, he fell short in defending his national title, finishing third in Veldhoven and also placing third at the World Championships in Tábor.
On January 1, 2015, Van der Haar moved to Team Giant-Alpecin. In the 2015/2016 season, he again won the Valkenburg World Cup, and for the first time, became European champion. In the 2016/2017 season, he added another World Cup victory, this time in Hoogerheide.
Since January 1, 2017, Van der Haar has been racing for Baloise Trek Lions, where he has been coached by former professional Sven Nys. The 2017/2018 season was dominated by Mathieu van der Poel, and competition became increasingly fierce for Van der Haar, preventing him from winning any World Cups for several consecutive years. In the Dutch National Championships, he consistently finished behind Van der Poel.
Fortunately for Van der Haar, both Van der Poel and Wout van Aert began focusing more on road racing, which reduced their cyclo-cross appearances and increased Van der Haar's chances. In the 2021/2022 season, he finally won another World Cup after a five-year gap and claimed his second European championship title. He also regained the national title that season. In the 2022/2023 season, Van der Haar achieved a remarkable feat by winning the overall Superprestige classification without winning any of its eight races. He also won his fourth Dutch national title.