Olli started professionally karting in 2012, competing in championships in Britain, taking part in championships like the 2016 Rotax Max Challenge Grand Finals – Junior.
He made his single seater debut in ADAC Formula 4 in 2017 with ADAC Berlin-Brandenburg. He was only a guest driver for the championship driving in Oschersleben and Nürburgring. Along with this, he raced in Italian Formula 4 (with selected rounds) and British Formula 4. For British Formula 4, he competed in 6 rounds, earning a total of 39 points. This placed him behind Manuel Sulaimán in the standings.
The following year in 2018, he raced in 3 championships: Italian Formula 4, ADAC Formula 4 and 2 rounds of Formula 4 UAE. For the UAE championship, he drove for Silberpfeil Energy Dubai. Here, he earned 3 wins and 4 podiums, putting his total points to 123 and finishing 7th in the standings. With Italian Formula 4 and ADAC Formula 4, he drove with Prema Theodore Racing, driving with Gianluca Petecof, Jack Doohan and Enzo Fittipaldi. For the Italian championship, he scored 262 points with 4 wins and 11 podiums, earning 3rd behind Leonardo Lorandi. In comparison, the ADAC Formula 4 championship left him in 7th with a win and 4 podiums. This time he was behind Mick Wishofer in the standings.
Alongside doing Formula championships, he also competed in endurance racing. For 2018, he competed in 12 hours of Yas Marina. Olli competed in GT4 with Bullit Racing. The race ended with him in 1st for his class.
For the 2019, he was retained by Prema but this time, in a new championship. Formula Regional European was formed as a step up from Formula 4 but behind Formula 3. Here, he competed alongside Frederik Vesti and Enzo Fittipaldi. He drove the car number 64. The season ended with him receiving 213 points with a win and 7 podiums under his name. He finished behind David Schumacher in 5th position.
Also during 2019, he competed in Intercontinental GT Challenge. For the first race, 12 hours of Bathurst, his teammate had a large crash in qualifying meaning the car was unable to compete in the race. The following race will be on the 23rd of July 2020 with the 24 hours of Spa.
FIA Formula 3 Championship
In 2019, Olli competed in the Macau Grand Prix with Trident. He qualified 17th, in which he finished 23rd behind Max Fewtrell. In the main race, Caldwell had to retire due to a broken suspension sustained before the 4th lap.
For the 2020 season, he was confirmed to be driving for Trident in the Formula 3 championship’s 2nd season, with Lirim Zendeli and Devlin DeFrancesco.