Flack made his karting debut in 2011 in the Bambino Queensland Cup, which he won in that year and in 2012. In 2014, he became a factory driver for CRG, and began karting internationally alongside in Australia. In 2016, he won the Macau International Kart Grand Prix, and began competing in World Series Karting the same year.[5] Switching to the Energy Course team in 2019, Flack won in the IAME International Final in the Junior ROK category,[6] and also competed in the FIA European Karting European Championship in the OK Junior class in this year.
In 2020, Flack was announced as one of two drivers to be representing Asia, Pacific and Oceania at the Ferrari Driver Academy scouting world final, alongside James Wharton.[7] He was a finalist in the event.
Formula 4
Prior to his competitive debut in 2021, Flack spent time in New Zealand in 2020 working as an engineer in the Toyota Racing Series to understand the mechanical side of racing better.[7]
Flack made his car racing debut in the 2021 F4 British Championship driving for Phinsys by Argenti,[8] following his participation in official British F4 tests in 2020 and tests with MTEC Motorsport. He also competed in select rounds of ADAC Formula 4 and the Italian F4 Championship.[9] He finished 11th in the British F4 season, with 3 overall podiums.