Piastri had won the 2019 Formula Renault Eurocup with R-ace GP in his first full European campaign, defeating Victor Martins by 7.5 points in a hard-fought final round at Yas Marina. He then joined Prema for the 2020 FIA Formula 3 Championship — the team having won the title the previous year — alongside former F4 rival Logan Sargeant and reigning Formula Regional European champion Frederik Vesti. He was simultaneously a member of the Renault Sport Academy. The 2020 season was delayed and shortened due to the COVID-19 pandemic.
Piastri opened the campaign with a feature race victory at the first Spielberg round, qualifying third and avoiding a first-corner collision. He retained the championship lead through the early rounds, extending his advantage to 25 points after back-to-back second-placed finishes in Budapest and the first Silverstone round.
The season tightened considerably from mid-point. At the second Silverstone round, reliability issues in qualifying restricted him to seventh and sixth. At Spa-Francorchamps, Sargeant extended his lead to seven points over Piastri following a sprint victory. The penultimate round at Monza saw Piastri reclaim the advantage: he climbed from fifteenth to third in the feature, though a retirement followed in the sprint after a collision with Clement Novalak and David Schumacher. Sargeant neutralised this with a late crash of his own with Vesti.
Entering the season finale at Mugello, Piastri held an eight-point advantage over Sargeant and 24 over Pourchaire. He carried a five-place grid penalty into the feature race and finished eleventh, unable to score. He entered the deciding sprint tied with Sargeant. Sargeant was eliminated in a first-lap collision with Lirim Zendeli; Piastri passed four drivers including Pourchaire for seventh. Pourchaire reclaimed the position under the safety car restart but could not close further ground with his podium finish. Piastri's seventh place was sufficient: he clinched the title by three points over Pourchaire and four over Sargeant.
Piastri's F3 title was the middle chapter of the most compressed junior ladder ascent seen in the modern era. He subsequently won the 2021 FIA Formula 2 Championship with Prema as a rookie, making him the only driver in history to win Formula Renault, Formula Three, and Formula Two in consecutive seasons. His 2020 season also served as the foundation for his appointment as Alpine's reserve driver for 2022 and his eventual move to McLaren in 2023.
The closeness of the 2020 championship — resolved at the final round by a handful of points across three drivers — reinforced a reputation for composure and consistency that would mark Piastri's career. His ability to manage a difficult final weekend, carrying a grid penalty, and still deliver the result under maximum pressure was noted by team principal Rene Rosin and became part of the Prema narrative around his development.
Theo Pourchaire, who narrowly missed out on the 2020 title, won the FIA Formula 2 Championship himself in 2023. Logan Sargeant made his Formula One debut with Williams in 2023.