2021

Barter began racing in cars in 2021, having signed up for the French F4 Championship. The first round at Nogaro brought immediate success, as the Australian took victory on Sunday, whilst the following event at Magny-Cours heralded a triple of podiums, bringing Barter into the championship fight. However, the middle part of the season would not yield the strongest results, with just two podiums coming his way in the space of four rounds, which meant that Barter had lost a lot of ground to fellow contenders Esteban Masson and Macéo Capietto going into the season finale. There, Barter showed some more good form, scoring a pair of podiums in the main races, and after a disqualification for Capietto, Barter inherited the win of the final race, which put him second in the standings.^[4]

2022

For the 2022 season, Barter opted to remain in Formula 4, citing his lack of pole positions and their importance in higher-level championships, such as Formula Regional, as a main reason for him to stay in the category.^[5] The Australian remained in French F4, whilst also competing for Campos Racing in the F4 Spanish Championship. In the latter, Barter started his campaign out strongly, being victorious in the season opener at Portimão.^[6] After this however, teammate Nikola Tsolov would become the dominant force within the championship, leading Barter to only take one podium from the subsequent two rounds.^[7] He would experience a more successful weekend at Spa-Francorchamps, finishing second in all three races to Tsolov, cementing himself in second place overall.^[8] At the next round in Aragón, Barter would add to his tally with two victories, as well as a third place in Race 2,^[9][10] before taking a hattrick of wins at Navarra, where he also took a pair of pole positions.^[11][12] By this stage, Tsolov had been crowned as the champion, with Barter ending his season by scoring two further podiums at Barcelona, securing himself the runner-up spot.^[13]

In the latter championship, the Australian proved his experience within the category by taking pole position for and winning the main races in Nogaro,^[14] before following that up with a win at the tricky Pau Circuit,^[15] taking the overall lead which he extended with another podium in Race 3 on the same weekend.^[16] Throughout the next four events, Barter would win seven races and take two more podiums in a dominant display at Lédenon,^[17][18] but he would be hindered from taking any points from the weekends at Spa and Valencia, as he had competed at those tracks during his Spanish F4 campaign, which meant that the Australian went into the season finale with a 32-point deficit to Alessandro Giusti.^[19] An early retirement in Race 1 meant an end for Barter's title ambitions, as, despite taking another podium on Sunday, he finished second in the championship.