In February 2018, Monger drove a single seater racing car for the first time since his crash when he tested a BRDC British Formula 3 car for the Carlin team at Oulton Park. The following month Monger confirmed that he would be racing for Carlin in the opening meeting of the 2018 BRDC Formula 3 series at the same venue. In order to compete in F3, he and his family had to appeal to the sport's international governing body, the Fédération Internationale de l'Automobile, to change their regulations, as they had restricted disabled drivers from racing single seaters on the grounds of safety: the FIA decided to lift the ban in December 2017, allowing disabled drivers to race appropriately-modified single seaters as long as they could pass safety checks. He finished third at Oulton Park in a car adapted for him: the modifications included moving the brake pedal upwards so he could brake using one of his leg stumps, and replacing the throttle pedal with a lever mounted on the steering wheel.
In June 2018, Monger drove a Formula 1 racing car for the first time when he tested a Sauber C30 at the Rockingham Motor Speedway in Corby. The car had been specially converted to match the hand controls present in the Carlin BRDC British Formula 3 car he races. A documentary feature about Monger's first Formula 1 drive was shown as part of Sky F1's coverage of the 2018 Austrian Grand Prix. Another documentary about Monger's career, Driven: The Billy Monger Story, was produced by the BBC and released via BBC Three in November 2018.