He made his car racing debut in the final three meetings of the 2017 Ginetta Junior Championship, driving with Elite Motorsport.

Following his successful stint in Ginetta Juniors, Foster moved to single-seaters when he joined Double R Racing for the 2019 F4 British Championship certified by FIA, powered by Ford EcoBoost season.

He followed that with a sublime weekend in Donington, winning two races and scoring a third-place finish in the other to give him a 17-point lead in the championship table.

In the opening qualifying session of the year, Louis set the benchmark and claimed double pole position in his debut weekend in the series.

Further success came at Brands Hatch when Foster scored three top-six finishes, including a third-place podium in the final race.

[10] The 17-year-old carried this momentum into the series' second visit to Donington Park, where he claimed another race victory, this time climbing from sixth on the grid, alongside two 11th-place finishes.

[11] Snetterton marked Foster's most successful weekend in the series to date as the Hampshire racer took his second double pole position of the season before converting those into his third win of the year and a further second-place podium alongside fourth and fifth in the additional two races.

Shortly after making his debut at Spa-Francorchamps, it was announced that Foster would also contest the rescheduled season finale at Circuit de Barcelona-Catalunya,[15] with the track hosting four races in lieu of the cancelled round at Circuito del Jarama.

[17] Starting from fourth in race three, the 17-year-old leapfrogged two cars on the first lap to take second place and another podium finish in the series, coming within touching distance of the win.