Louis began karting in 2008 in his home country, Switzerland, where he won the Vega Trofeo Super Mini Class the following year. Then in 2010, he claimed a third place finish in both the KF3 Bridgestone Cup Switzerland and Vega Trofeo Junior Categories before winning the latter in 2011. Following his years in karting, Delétraz moved to his single-seater career in 2012 and raced in the Grand Final of the Formula BMW Talent Cup season which was held at Motorsport Arena Oschersleben in Germany where he started from pole in all three races, taking a win on the second race. During the final race, Louis collided with fellow Swiss Ralph Boschung where both drivers retired.
Heading into 2013, Louis graduated into Formula Renault where he raced with Josef Kaifmann Racing at the Formula Renault 2.0 NEC Championship. His best race of the season was fifth, leaving him placing 19th overall in the championship. He continued with the team for a second FR2.0 NEC Season in 2014 where he won the opening race of the season in Monza. He took a further four podium positions, finishing as runner up in the championships and only 16 points from first place. During his time, he also made his debut in the Eurocup Formula Renault 2.0 Championship and took part in the rounds at Spa-Francorchamps, Nürburgring and Paul Ricard as a guest driver.
For 2015, he raced a dual campaign in both Eurocup Formula Renault 2.0 and Formula Renault 2.0 NEC where he remained with Josef Kaifmann Racing. Delétraz took home three race wins in the former while taking home four victories in the latter. During April, Louis was announced as one of the four drivers who were selected to join the BMW Motorsport Junior Programme. To finish off his year, he made his debut in the Formula Renault 3.5 Series at the fifth round in the Red Bull Ring, driving for Comtec Racing team. He soon graduated to Fortec full time for the 2016 season, finishing as runner up in the standings. In November 2016, Louis made his debut with Carlin in the final round of the GP2 Series.
FIA Formula 2
In December of 2016, Delétraz took part in the post-season testing with Racing Engineering before signing to race full-time along side them in the 2017 season with team mate Gustav Malja. He finished his season off with 16 points, placing him 17th in the Championship before moving to Charouz Racing System with Antonio Fuoco. He took home 74 points, placing him 10th with podiums in both Monaco and Paul Ricard. Entering into his third year of F2, Louis partnered up with Carlin to compete in the 2019 season with team mate Nobuharu Matsushita. He finished the season with two more podiums in Monaco and Silverstone sprint races, leaving him 8th in the standings.
The 2020 season of FIA Formula 2 will be Louis’ fourth year competing and he’s making his return to Charouz Racing System where he’ll compete with one of this years rookies, Pedro Piquet who placed fifth in the 2019 FIA Formula 3 Championship.