Ekström debuted in karting in 1993 before progressing through the Renault 5 Turbo Cup, which he won in 1996. He moved to the Swedish Touring Car Championship in 1997, finishing runner-up in a Volvo 850. After driving a Ford Mondeo in 1998, he won the 1999 STCC title in an Audi A4 quattro. A factory Volvo S40 drive in 2000 yielded a third-place finish before his transition to the Deutsche Tourenwagen Masters.
Ekström joined the Abt Junior team in the DTM in 2001, driving an Audi TT and finishing eighth on debut. He improved to third in 2002 and fourth in 2003, establishing himself as a consistent frontrunner. In 2004, he claimed his first DTM title, defeating Mercedes rivals Gary Paffett and Christijan Albers. After finishing second behind Paffett in 2005, he won his second DTM championship in 2007 following a difficult 2006. He competed in the DTM until his retirement from the series in 2018.
Ekström made his World Rally Championship debut in 1999 and recorded his best WRC result at the 2005 Swedish Rally, finishing tenth driving a Škoda Fabia WRC with the factory team. While his WRC outings remained limited, his broader rallying pedigree included winning the Henri Toivonen Memorial Trophy and Race of Champions titles that underscored his all-surface capability.
The Race of Champions became a recurring stage for Ekström's cross-discipline dominance. At the 2005 Race of Champions, he won the Nations' Cup alongside Tom Kristensen. In 2006, he earned the Champion of Champions title by defeating Sébastien Loeb in the individual finals. He repeated as Champion of Champions in 2007, beating Michael Schumacher, and won the Race of Champions again in 2009, once more defeating the seven-time Formula One world champion.
In June 2010, Ekström became one of the first Scandinavian drivers to start in the NASCAR Sprint Cup Series, substituting for Brian Vickers at Infineon Raceway for Team Red Bull. He drove the No. 83 Toyota Camry and finished 21st while leading seven laps, spending much of the race inside the top ten. He made a further Sprint Cup start at the Air Guard 400 at Richmond International Raceway. In 2013, he co-drove with Andy Priaulx at the Bathurst 1000 as a wildcard entry, qualifying nineteenth and finishing tenth.
Following in his father Bengt's footsteps, Ekström branched into rallycross in 2013, finishing second in the Swedish round of the European Rallycross Championship in a Volkswagen Polo. He then established his own EKS RX team to compete in the inaugural FIA World Rallycross Championship from 2014, fielding Audi S1s. He ultimately claimed the FIA World Rallycross Championship title, cementing his status as a world-class competitor on dirt and tarmac alike. After Audi withdrew its works program at the end of 2018, the team scaled back to a privateer entry.
Ekström extended his reach into electric motorsport by joining Cupra x Zengő Motorsport for the inaugural Pure ETCR (later FIA ETCR) season, winning Cupra's home event in Spain and clinching the drivers' title. In the 2021 Dakar Rally he made his first rally-raid attempt in a Yamaha side-by-side vehicle, gaining experience despite technical difficulties. Audi announced him as a works Dakar driver alongside Carlos Sainz and Stéphane Peterhansel for their innovative RS Q e-tron hybrid project.
At the 2022 Dakar, Ekström and navigator Emil Bergkvist won one stage and finished ninth overall in the Audi RS Q e-tron. The 2023 Dakar proved difficult as all three Audi entries suffered misfortunes; Ekström finished fourteenth. The 2024 Dakar saw a promising campaign interrupted by a technical issue, after which Ekström acted as support car for teammate Sainz, who ultimately won overall. After the end of his Audi programme, Ekström signed with M-Sport Ford for their Dakar effort. In the 2025 Dakar, competing in the new Ford Raptor T1+, the Ekström–Bergkvist crew climbed into the top three early, won a stage, and finished third overall — his strongest Dakar result. They repeated the third-place finish at the 2026 Dakar.
Ekström's career is defined by an extraordinary breadth of top-level success across touring cars, rallycross, endurance racing, NASCAR, electric touring cars, and rally raid. His willingness to debut in unfamiliar disciplines at the highest level — and consistently deliver strong results — marks him as one of the most versatile drivers in modern motorsport history.