Kenyon attended his first auto race in 1946 and began his own racing career in 1954, starting in a 1937 Chevrolet Coupe before progressing to modified stocks in 1955. He transitioned to midget cars in 1958. His first championship came in NASCAR's Florida midget series in 1962, but he switched to USAC mid-season and finished fifth in the national points. He won the Turkey Night Grand Prix in 1963 and his first USAC National Midget championship in 1964.
In June 1965, during a USAC IndyCar race at Langhorne Speedway, Pennsylvania, Kenyon's engine failed and sprayed oil across the car and the track. He lost control, struck the wall, and was knocked unconscious. Two other drivers — Jim Hurtubise and Ralph Liguori — slid on the oil and struck Kenyon's fuel tank, igniting a fire. Joe Leonard pulled Kenyon from the burning car. The injuries were severe: Kenyon suffered burns over much of his body and lost nearly all the fingers on his left hand.
Treatment took place at the San Antonio Burn Center, and Kenyon underwent multiple operations. The recovery appeared to spell the end of a promising career. Instead, Kenyon, his brother Don, and their father Everett devised a custom glove with a rubber grommet stitched into the palm that could hook directly onto the steering wheel — turning a disability into a workable adaptation. The three of them formed 3-K Racing, with Don serving as crew chief.
Kenyon returned to racing in 1966, less than a year after the accident, qualifying for his first Indianapolis 500 just eleven months after the fire and finishing fifth. His recovery became one of motorsport's most celebrated stories. Over the following decades, he accumulated seven USAC National Midget championships, winning the title in 1964, 1967, 1968, and beyond through the 1980s, with his final USAC National Midget championship coming in 1985. He was inducted into the National Midget Auto Racing Hall of Fame in 1984, a year before that last title.
In 1967, Kenyon won 17 of 49 features to claim the national midget crown. In 1968, he finished third in the Indianapolis 500 in a car sponsored by his hometown of Lebanon, Indiana, and won the national midget championship the same year — despite routinely rebuilding the Offenhauser engine himself despite his hand injuries. He took fourth at Indianapolis in 1969. His eight Indianapolis 500 appearances yielded four top-five finishes, a remarkable record.
At his Motorsports Hall of Fame induction in 2003, Kenyon's USAC National midget totals stood at 111 feature wins, 131 seconds, 107 thirds, 81 fourths, and 69 fifths — a total of 419 top-five finishes from 688 top-ten results. Including wins in Australia and New Zealand and regional events, he had accumulated more than 380 total midget feature victories.
Kenyon had seven USAC National Midget championships, eight runner-up finishes in the season standings, and top-five points finishes in 21 of 27 seasons between 1966 and 1988. He competed in 65 USAC Championship (IndyCar) car races across his career.
His longevity was exceptional. When his wife Marieanne suffered a serious head injury in a bicycle accident in 1995, Kenyon withdrew from national tour racing to care for her. Even so, he continued to race in the regional NAMARS championships, winning titles in 1995, 1996, and 1997 — while in his sixties. He returned to compete at Indianapolis Speedrome past his 70th birthday in 2003, and ran the full schedule there in 2005 against his son Brice Kenyon, who had won the 2004 Speedrome midget track championship.
Kenyon won the Turkey Night Grand Prix a second time in 1975, on the 605 Speedway on pavement — the first time the historic event had been held on a paved surface. He won the Indianapolis Speedrome midget track title in 1993.
Indianapolis Raceway Park hosts the annual Mel Kenyon Classic midget car race in his honor, an event Kenyon himself competed in during the 2000s. He was inducted into the Motorsports Hall of Fame of America in 2003 and the International Motorsports Hall of Fame in 2003. The Motorsports Hall of Fame of America's characterization of him as potentially midget car racing's greatest driver ever reflects both the statistical breadth of his record and the remarkable personal story that shaped it.