Wittmann began karting at age six, claiming the 2004 German Junior Karting Championship before transitioning to car racing in 2007 with Josef Kaufmann Racing in Formula BMW ADAC. He won two races in his debut season and finished fifth in the standings. For 2008 he moved into the newly formed Formula BMW Europe, scoring eleven podiums including one victory, but was narrowly beaten to the title by teammate Esteban Gutiérrez.
Progressing to Formula 3 in 2009 with Mücke Motorsport in the Euro Series, Wittmann struggled in a competitive field and finished sixteenth in the standings. He switched to Signature for 2010, winning at Hockenheim and accumulating ten podiums to finish second overall. His third year in the series, in 2011, brought thirteen podiums and five wins including victories at the Pau Grand Prix and two at the Norisring, though Roberto Merhi and the Prema Powerteam were dominant and Wittmann finished second once again. He also took second at the Masters of Formula 3 and pole at Macau, finishing third in the race.
After conducting DTM tests for BMW at the end of 2011, Wittmann was signed as BMW's official test driver for 2012 and also competed in GT3 endurance events, including a ninth-place finish at the 24 Hours of Nürburgring. His full DTM debut came in 2013 with Team MTEK in a BMW M3 DTM. He scored points in his first two starts, took second place at the Red Bull Ring, claimed a pole at Zandvoort, and finished eighth in the standings — the highest-placed rookie.
Joining Team RMG for 2014, Wittmann launched his title challenge immediately, winning at the opening Hockenheim round. After an off in the rain at Oschersleben he returned with a dominant victory at the Hungaroring to reclaim the championship lead. Wins at Spielberg and the Nürburgring followed, and Wittmann secured the DTM drivers' title at the third-to-last event with a sixth-place finish, ending the year 50 points clear of runner-up Mattias Ekström.
The 2015 season, now contested over two-race weekends, began poorly with only three points finishes in the first six races. Wittmann recovered with victory at Zandvoort and further podiums but ultimately finished sixth overall. During the summer he was invited to test the Toro Rosso STR10 Formula One car at the Red Bull Ring, earning praise from race engineer Phil Charles for his technical feedback and consistency.
In 2016, Wittmann won from pole at Spielberg and then reeled off a nine-race points-scoring streak. Victories in Moscow and at the Nürburgring put him in commanding position, though a disqualification for a technical infringement in Hungary cut his lead over Edoardo Mortara to 14 points. He managed the situation expertly at the Hockenheim finale — finishing second on Saturday and fourth on Sunday, both times ahead of Mortara — to clinch his second DTM title.
Wittmann's 2017 campaign included a luckless run of early bad luck and a notable public critique of Audi's drivers over team radio, but he recovered in the second half of the year to win at the season finale and finish fifth. In 2018 he placed fourth overall after wins in Hungary and at the Norisring.
The 2019 Class 1 season saw Wittmann emerge as one of the title contenders. He won at Hockenheim, Zolder, Misano, Assen, and Brands Hatch — five victories that briefly put him in the championship fight against René Rast and Nico Müller — before fading to third in the standings over the final rounds. The 2020 season, the last of the DTM's Class 1 era, was his most difficult in the championship; he finished only three times on the podium and placed ninth overall as Audi dominated comprehensively.
When the DTM adopted GT3 regulations for 2021, Wittmann moved to Walkenhorst Motorsport. He won at Zolder and finished fourth in the standings after a consistent first half-season was undermined by two non-scores at Hockenheim in the second half. He also achieved his maiden podium at the 24 Hours of Nürburgring that year, finishing second for Rowe Racing.
In 2023 Wittmann competed across three disciplines simultaneously: the DTM at Project 1 (where the team's impending bankruptcy hindered results), the GT World Challenge Europe Endurance Cup with ROWE Racing where his trio won at Monza and triumphed at the 24 Hours of Spa, and the IMSA SportsCar Championship's new GTP class for BMW.
For 2024, Wittmann joined Schubert Motorsport in the DTM alongside René Rast and Sheldon van der Linde, and was selected for BMW M Team WRT's FIA World Endurance Championship Hypercar programme, partnering Raffaele Marciello and Dries Vanthoor.
Wittmann is the driver most closely associated with BMW's competitive DTM years in the mid-2010s. His two titles made him the only BMW driver to claim the DTM championship in the V8 era's final years, and his versatility in adapting to GT3 and Hypercar machinery after 2020 demonstrated the depth of his craft beyond the touring car discipline.