Crichton-Stuart was born in Rothesay into one of Scotland's oldest aristocratic families. His father was the 6th Marquess of Bute, and his courtesy title as heir was Earl of Dumfries — the name by which he raced. He was educated at Ampleforth College, which he left at sixteen to pursue motor racing. The family's ancestral seat, Mount Stuart House on the Isle of Bute, was where he and his siblings were raised.
In 1984, Dumfries announced himself as one of the most electrifying single-seater talents in Britain, winning 14 races to claim the British Formula 3 Championship in dominant fashion for Team BP (Dave Price Racing). That same season he finished runner-up to Ivan Capelli in the European Formula Three Championship, reinforcing his reputation as a driver of exceptional pace.
In 1985, Dumfries moved to the newly created FIA International Formula 3000 Championship. He raced first for Onyx Race Engineering before switching to Lola Motorsport. The season proved disappointing; a sixth-place finish at Vallelunga was his best result in a campaign that failed to replicate his Formula 3 form.
Dumfries earned a Formula One drive for 1986 with JPS Team Lotus, joining the team as a late addition in circumstances linked to Ayrton Senna's preference not to have Derek Warwick as a teammate. He contested 15 Grands Prix — not qualifying at Monaco — with the Lotus 98T, which was powered by turbocharged Renault engines. He scored three championship points across the season and generally ran in the midfield, comparable in pace to Tyrrell's Martin Brundle and Philippe Streiff. After one season, he was replaced by Satoru Nakajima as part of Lotus's new arrangement to use Honda engines.
The defining moment of Dumfries's racing career came in June 1988, when he co-drove a Jaguar XJR-9 for Tom Walkinshaw's Silk Cut Jaguar Team to overall victory at the 24 Hours of Le Mans. His co-drivers were Jan Lammers of the Netherlands and Englishman Andy Wallace. The win was a landmark result for Jaguar, marking the British manufacturer's return to the top of endurance racing after a long absence.
He also appeared in the 1988 British Touring Car Championship, taking part in the one-hour endurance race at Donington Park alongside Guy Edwards for Andy Rouse's Kaliber Racing team, driving a Ford Sierra RS500 to third place overall and in Class A.
In 1993, Dumfries succeeded his father and became the 7th Marquess of Bute. Thereafter he was more widely known as John Bute. He was ranked 616th in the Sunday Times Rich List in 2008, with an estimated fortune of £125 million. His ancestral holdings included Mount Stuart House on the Isle of Bute and, until 2007, Dumfries House in Cumnock, Ayrshire — the latter sold to a trust later known as The King's Foundation for £45 million.
Dumfries married Carolyn Waddell in 1984; the couple divorced in 1993 and had three children. In 1999 he married fashion designer Serena Wendell, with whom he had a daughter. He died of cancer in March 2021.
Johnny Dumfries remains one of the most accomplished British racing drivers of the 1980s. His 1984 British F3 title was among the most dominant performances the championship had seen, and his 1988 Le Mans victory with Jaguar secured his place in endurance racing history. The combination of a single Formula One season and overall Le Mans honours makes his career an unusual arc — aristocratic privilege, early promise, a brief top-level single-seater career, and a crowning triumph in the sport's most celebrated endurance race.