Lewis-Evans was born in Luton, Bedfordshire, but grew up in Kent, where his father, Lewis "Pop" Lewis-Evans, owned and operated a garage business. Pop Lewis-Evans had previously worked as a mechanic for the well-known racing driver Earl Howe, though he had not raced himself. On leaving school, Lewis-Evans served a three-year apprenticeship at Vauxhall Motors in Bedfordshire before being called up for National Service, during which he served as a motorcycle despatch rider for the Royal Corps of Signals.
Lewis-Evans began racing in 1951 with a Cooper 500 Formula 3 car, often encouraged by and racing against his father. He achieved numerous wins and podium finishes across the 500cc category, continuing in that class until 1956. In the later years of this period, his engines were prepared by Francis Beart. A notable result came in May 1954 at the Nurburgring, where Lewis-Evans finished second behind Stirling Moss in a 1–2 for Cooper-engined cars, with Moss driving a Beart Cooper and Lewis-Evans in a Cooper with a Beart-prepared engine.
In 1957 Lewis-Evans won the Glover Trophy at Goodwood, a non-championship race run to Formula One rules. His Formula One World Championship debut came at the 1957 Monaco Grand Prix driving a Connaught Type B. Despite the car's relative inferiority, he finished fourth, beaten only by Fangio, Tony Brooks, and Masten Gregory in the dominant Maserati 250F. The performance brought him to the immediate attention of Tony Vandervell, owner of the Vanwall team.
By the following Grand Prix Lewis-Evans was driving the third Vanwall alongside Stirling Moss and Tony Brooks. The 1957 Vanwall was quick when its engine held together, though reliability proved inconsistent. Lewis-Evans's best result that year came at the non-championship Moroccan Grand Prix, where he finished second. At the Italian Grand Prix — the final World Championship event of the season — he took pole position but retired with engine problems.
The 1958 Formula One season proved significantly stronger for the Vanwall team. Moss and Brooks each took three victories, with Moss also winning the season opener in Rob Walker's Cooper. Lewis-Evans contributed meaningfully to the championship effort: he took pole position at the Dutch Grand Prix, though he failed to finish; secured podium finishes in Belgium and Portugal; and scored a fourth place at the British Grand Prix. His podiums in Belgium and Portugal did not add to Vanwall's constructors' points haul — those races were won by Vanwall drivers — but they reduced the points available to rival manufacturers. He ended the season ninth in the World Drivers' Championship with 16 points.
At the season-ending Moroccan Grand Prix, held at the dusty Ain-Diab Circuit, Lewis-Evans's engine seized and sent him into barriers at high speed. The car caught fire. He was airlifted back to the United Kingdom but died from his burns in hospital six days after the accident, on 25 October 1958.
Lewis-Evans's death cast a pall over Vanwall's victory in the 1958 International Cup for F1 Manufacturers, a title to which he had contributed significantly. Tony Vandervell, deeply affected by the loss, withdrew from motorsport entirely at the end of the 1958 season. Lewis-Evans's career — ending at just 28 — left behind two pole positions, two podiums, and the memory of a driver who had risen rapidly from club racing to the front of Formula One's grid in only two seasons.