Reynolds began motorsport competition in 2003, contesting the Australian Formula Ford Championship before joining Sonic Motor Racing Services for a four-year programme. He won the 2004 Australian Formula Ford Championship and then transitioned into Porsche Carrera Cup Australia, where he claimed the 2007 title after a season-long battle with Alex Davison and Craig Baird.
Alongside his Carrera Cup campaign, Reynolds took endurance co-driver roles in the Supercars Championship from 2007 onward, gaining experience with Paul Weel Racing and then Tony D'Alberto Racing before landing a full-time seat with Walkinshaw Racing in 2009.
Reynolds spent the early part of his full-time Supercars career building a reputation as a quick but unlucky driver. Seasons at Walkinshaw Racing, Kelly Racing, and then Rod Nash Racing from 2012 to 2015 produced steady progress. His second place at the 2012 Bathurst 1000 — just 0.786 seconds behind winner Jamie Whincup, a record margin at the time — announced him as a genuine frontrunner. He took his first Supercars race win at the 2013 Gold Coast 600 when race leader James Courtney suffered a suspension failure, and added further victories in subsequent seasons including a solo win at Hidden Valley in 2015 while still at Rod Nash Racing. Reynolds finished third in the 2015 championship, the best result of his time with Prodrive Racing Australia.
Reynolds joined Erebus Motorsport for the 2016 season as the team rebuilt itself after departing from the Mercedes GT programme. The first year was difficult as the operation relocated to Melbourne and ran older Holden Commodore machinery, but Reynolds and engineer Alistair McVean began unlocking real pace.
In 2017, Reynolds delivered the defining result of his career. At the Bathurst 1000, he and Youlden navigated a treacherous, rain-affected race to secure victory for Erebus Motorsport — the first independent Australian team to win the race since Garry Rogers Motorsport in 2000. Reynolds held off Nick Percat in the closing laps after the two leading cars spun at the final corner in wet conditions.
The 2018 season was arguably his most consistently competitive, with race wins including a spectacular outside pass on the first corner at Hidden Valley. Reynolds came within reach of the Bathurst 1000 title again that year but fatigue in the late stages cost Erebus a chance at back-to-back victories. He finished fifth in the championship and remained a top-ten fixture until his departure from Erebus after 2020.
Reynolds moved to Kelly Grove Racing for 2021, bringing primary sponsor Penrite with him and continuing under the Grove Racing banner after their takeover of the team. He remained with the team through 2023 before joining Team 18 for the 2024 season, replacing Scott Pye in the No. 20 Chevrolet Camaro ZL1.
Reynolds is one of the most recognizable personalities in Supercars, as well known for his irreverent off-track humor — including throwing a television microphone into the crowd after his maiden win and performing a podium "shoey" before Daniel Ricciardo made the gesture globally famous — as for his speed. His 2017 Bathurst 1000 victory stands as one of the landmark results for an independent team in the modern era of Australian touring car racing.
At the 2015 Bathurst 1000, Reynolds was fined AU$25,000 for making sexist remarks regarding the all-female entry of Simona de Silvestro and Renee Gracie. In 2021, Reynolds missed two Supercars rounds at Sydney Motorsport Park after failing to meet New South Wales Health COVID-19 vaccination requirements.