In 2016, Caldwell competed in his first competitive series outside karting where he drove for JHR Developments in the Ginetta Junior Championship. He drove thirteen races where he finished one place behind his current F3 rival Enzo Fittipaldi in 19th.
In 2017 made his debut in ADAC Formula 4 with the ADAC Berlin-Brandenburg e.V. team. Caldwell didn't finish in any points scoring positions however he was ineligible for points due to the fact he was a guest driver. His highest finish that year was 17th at the Nürburgring. In 2018 he made the full-time switch to Prema where he finished in 7th on 125 points, stepping on the podium four times and one of them at Oschersleben he stepped on the top step.
British F4
In 2017, Caldwell finished 14th for Arden with 39 points. His highest finishing position was 7th which he recorded three times.
Italian F4
was the team Caldwell made his Italian f4 debut for in 2017. In the fifteen races he competed in he recorded ten points helping him to 11th in the championship, 273 points behind champion Marcus Armstrong. In 2018 Caldwell switched to the Italian team Prema where he recorded eleven podiums, four of which were wins. Caldwell was one of two drivers to win all 3 races in a weekend. He did this at Vallelunga, Enzo Fittipaldi also achieved this at Misano. Caldwell finished a career best 3rd in this season.
F4 UAE
For the 2017–18UAE Formula 4 season, Caldwell raced for Silberpfeil Energy Dubai. Caldwell only competed in the first two rounds where he won 3 races and had 4 podiums which gained him 123 points and 7th in the championship.
On 4 November2019, Caldwell announced he will be racing for the Trident team at the 2019 Macau Grand Prix. Caldwell qualified 17th, 1.6 seconds behind pole-sitter Jüri Vips with a time of 2:06.641. In the qualifying race Caldwell got caught up in an incident at the start where Sargeant braked later than other drivers and his front wing glanced Maini's rear-right wheel. Maini was sent into a spin and rested against a trackside wall in a way that caused his vehicle to protrude at the exit of Lisboa turn, Caldwell ended up stationary briefly meaning he lost position. In the end he finished in 23rd meaning he started the race near the back. At the start of the race Caldwell made contact with Andres Estner and on the fourth lap, Caldwell retired from the consequences of the earlier collision that damaged his front wing and a tyre.
