Born Willem Edouard Numa Ghislain Mairesse, the Belgian driver was known for a burning competitive drive that unsettled even fellow professionals. Peter Revson, watching Mairesse prepare for a race at Spa, described looking into his car and seeing a furrowed face and eyes that seemed to change color — "almost like looking at the devil." Mairesse's aggression was as much a strength as a liability throughout his career.
He announced himself in rallying before turning to circuit racing, winning the grueling Liege-Rome-Liege marathon rally in 1956.
Mairesse established himself as one of Ferrari's most valued sportscar drivers through the early 1960s. In June 1959 he secured third place in the Grand Prix of Monza, finishing behind Alfonso Thiele and Carlo Abate, both also in Ferraris.
At the 1961 24 Hours of Le Mans, Mairesse and British driver Mike Parkes finished second to Phil Hill and Olivier Gendebien, while also eclipsing the previous Le Mans distance record by covering 2,758.66 miles in their Ferrari 250 TR/61. The 1963 season was particularly active: Mairesse and Nino Vaccarella finished second at the 12 Hours of Sebring behind teammates Ludovico Scarfiotti and John Surtees; then Surtees and Mairesse won the 1000 km of the Nürburgring in a Ferrari 250P. The same pairing led for fifteen of the eighteen hours of the 1963 24 Hours of Le Mans before their car caught fire while Mairesse was driving. He escaped uninjured.
Mairesse won the 1964 Grand Prix of Angola in Luanda and piloted a Ferrari 250 LM to victory in the 500 km sportscar race at Spa in May 1965. At the 1965 24 Hours of Le Mans, Mairesse and Jean Beurlys finished third overall in a Ferrari 275 GTB, winning the GT category in that class's Le Mans debut. In May 1966, Mairesse and Herbert Mueller drove a Porsche Carrera 6 to victory in the Targa Florio, with rain causing such attrition that only thirteen of seventy starters finished. Mairesse and Beurlys again reached third at the 1967 24 Hours of Le Mans, won that year by Dan Gurney and A.J. Foyt.
Mairesse contested 13 World Championship Grands Prix. He debuted on 19 June 1960 and achieved his best result — a third-place finish — at the 1960 Italian Grand Prix at Monza, a race won by Phil Hill with Richie Ginther second.
At the 1962 Belgian Grand Prix at Spa, Mairesse qualified fifth and engaged in a fierce battle with Trevor Taylor's Lotus, the two cars passing and repassing for more than an hour. In the long Blanchimont sweeper the cars made contact at over 100 mph; Mairesse's Ferrari left the road, careened into a hillside, and caught fire after flipping over. He was thrown clear, losing his shoes and trouser legs, but escaped without serious injury. In the 1962 Italian Grand Prix he came fourth, finishing barely a car's length ahead of Giancarlo Baghetti. He scored a total of seven championship points over his Formula One career.
The 1963 German Grand Prix at the Nürburgring ended his F1 season when his Ferrari overturned after leaving the track, leaving him with a broken arm. His teammate Surtees won that race.
Mairesse entered the 1968 24 Hours of Le Mans co-driving a Ford GT40 with Jean Blaton, who raced under the pseudonym "Beurlys." At the chaotic standing start, Mairesse is believed to have failed to close his door properly. As he reached the end of the Mulsanne Straight on the first lap, the door flew open and he lost control, crashing violently into roadside trees. He suffered head injuries, broken bones, and severe burns, and was left in a coma for more than two weeks.
Mairesse survived the injuries, but suffered physical and mental impairments that prevented him from ever returning to racing. He fell into depression over the end of his career, and on 2 September 1969 — less than twelve months after the accident — he took his own life by overdosing on sleeping pills in a hotel room in Ostend at the age of forty.