McErlean made his rally debut in 2014, entering the Junior Turkey Run in Northern Ireland alongside his cousin Thomas and winning on their first start in a Peugeot 107. In 2015, the pair won the Junior 1000 Rally Challenge in Northern Ireland, recording four victories, and defended the title the following year while simultaneously winning the Junior 1000 series in Great Britain with six wins from eight starts.
In 2017, McErlean moved into the British Rally Championship with a Citroën C2 R2 Max but suffered reliability problems, finishing ninth in the junior standings. He drove a Ford Fiesta R2T for 2018, finishing 11th in the British Junior class. His 2019 season in a Peugeot 208 R2 proved a turning point: McErlean won his class at the West Cork Rally, Pirelli International Rally, and Ulster Rally, clinching the junior title a round early while finishing third overall. His form earned support from Hyundai and a WRC debut at Wales Rally GB in a Hyundai i20 R5, though he retired on stage six with a mechanical failure.
With backing from Motorsport Ireland, McErlean was set for the 2020 British Rally Championship with Hyundai before the season was largely cancelled due to the COVID-19 pandemic. He contested the final two rounds of the European Rally Championship before finishing the year with a WRC3 entry at Rally Monza, where he and co-driver Keaton Williams placed seventh in class.
In 2021, McErlean joined the Hyundai Motorsport junior driver programme. After finishing third overall at the Olympus Rally in the United States, he claimed fifth at his first WRC3 appearance of the year in Portugal. Three more rounds alongside new co-driver James Fulton yielded two further top-five finishes, including third at the Rally Catalunya. He ended the season ninth in the WRC3 drivers' standings.
McErlean stepped up to WRC2 in 2022 with Hyundai and Fulton. The season was difficult, with only a single top-ten finish in Estonia. He remained with Hyundai in 2023, making his Monte Carlo debut alongside new co-driver John Rowan before an exhaust issue ended his challenge on day two. McErlean and Fulton withdrew from their next scheduled event in Croatia as a mark of respect following the death of compatriot and Hyundai colleague Craig Breen. A seventh in class in Portugal was followed by a return to Fulton from the ERC round in Latvia onwards, with McErlean finishing 26th in the WRC2 standings and scoring his season-best fourth at the Latvia ERC event.
For 2024, McErlean joined Toksport in a Škoda Fabia RS Rally2 in WRC2. He claimed his maiden WRC2 podium — second in Portugal — and challenged for the top again at Rally Italia Sardegna before a puncture intervened. After crashing in Poland on the penultimate stage, he recovered to deliver consistent results across his remaining four championship-listed events, never finishing outside the top eight. McErlean ended the season ninth in WRC2.
In December 2024, McErlean and Fulton were announced as M-Sport Ford World Rally Team drivers for the 2025 WRC season in the Rally1 class, joining Grégoire Munster in the team's lineup. McErlean made a composed debut, finishing seventh at the Monte Carlo Rally — a mature result on one of the championship's most technically demanding events.
McErlean's rise from Junior 1000 events to a factory WRC seat in under a decade reflects both his natural pace and his methodical progression through international rally structures. His signing by M-Sport Ford confirmed him as one of the most promising Irish rally drivers of his generation.