Brabec was born in San Bernardino and began BMX cycling at age five. When he was fifteen his family moved to Hesperia, California, a high-desert community in the Mojave whose landscape shaped his orientation toward off-road competition. After trying motocross, he turned to desert racing in 2011.
He announced himself as a dominant force in American off-road racing in 2014, sweeping the Baja 1000, the Baja 500, and the San Felipe 250 in a single season, alongside the Hare and Hound AMA Championship, the Vegas to Reno, and the SCORE International Pro Motorcycle title. The scale of that 2014 season drew Team HRC's attention.
Honda brought Brabec to the Abu Dhabi Desert Challenge in 2015 — his first international participation — where he was the top junior and finished fifth overall. He made his Dakar Rally debut in 2016, finishing ninth.
In 2017 Brabec won his first Dakar stage but failed to finish the race. He retired again in 2018 while running sixth, and suffered a third consecutive DNF in 2019. Three successive retirements, each at progressively higher competitive standing, made the breakthrough feel a matter of time.
At the 2020 Dakar Rally — the first edition held in Saudi Arabia — Brabec won the motorcycle category with two stage victories, becoming the first American in history to win the bike division. The result also ended a lengthy drought for Honda, whose last bike-category victory had come in the 1990s. He carried race number 9 on a Monster Energy Honda HRC machine.
In 2021 he returned and finished second overall with four stage wins. He placed seventh in 2022 and was forced to withdraw from the 2023 event following a crash. At the 2024 Dakar Rally he claimed his second title, leading from Stage 6 through to the finish and winning by a margin of 10 minutes and 53 seconds over Ross Branch.
In the 2025 Dakar Rally Brabec finished fifth, competing without being fully recovered from a crash at the preceding Rallye du Maroc. Across the 2025 FIM World Rally-Raid Championship season he added second at the Abu Dhabi Desert Challenge, third at the Rallye du Maroc, third at the South African Safari Rally, and fourth at the BP Ultimate Rally-Raid Portugal, finishing third in the W2RC overall standings. He competed at the 2026 Dakar Rally and finished second.
Brabec has been a consistent top-level presence since the FIM W2RC's formation. Beyond the Dakar, notable results include winning the Rallye OiLibya du Maroc in 2017, third in Morocco in 2018, fifth in 2019, and winning the Desafío Ruta 40 in 2024. He has also won the Sonora Rally in 2019 and 2020 and Vegas to Reno on multiple occasions.
Away from rally raid, Brabec represented the United States at three International Six Days Enduro events, the oldest annual off-road motorcycle competition sanctioned by the FIM.
Brabec's 2020 victory ended American drought at Dakar stretching across multiple decades. Prior to his win, no American had stood on the top step of the motorcycle podium in the event's history. His second title in 2024 — won with a dominant final week — confirmed his position as one of the premier rally raid riders of the Saudi Arabia era. He rides for Monster Energy Honda HRC carrying race number 9.