Flock was present at NASCAR's inaugural Strictly Stock race in 1949 at Charlotte, North Carolina, finishing fifth in an Oldsmobile 88 he borrowed from his newlywed neighbors. The first official season closed with all three Flock brothers in the top eight of the points standings. Flock claimed his first official NASCAR race victory in 1950 at Charlotte and steadily built momentum through the early 1950s, winning seven races in 1951 and eight in 1952.
His relentless 1952 campaign earned him his first NASCAR Grand National Championship, finishing 106 points clear of Herb Thomas despite flipping in the final race at West Palm Beach. Flock later quipped he was "the only driver to ever win a championship upside-down."
The 1953 season produced one of racing's most improbable footnotes. On May 16, 1953, Flock won at Hickory Motor Speedway with a rhesus monkey named Jocko Flocko riding along in a specially built seat — making the monkey the only non-human co-driver ever to share in a NASCAR Grand National win. The arrangement ended two weeks later at Raleigh when Jocko triggered the tire-observation device on the right front wheel, was struck by a pebble, and forced an unscheduled pit stop that cost Flock a likely victory.
The 1955 season stands as Flock's career masterpiece and one of the most dominant individual campaigns in NASCAR history. Driving for car owner Carl Kiekhaefer, Flock won 18 of 45 races — a record that stood until Richard Petty broke it in 1967 — and secured 19 pole positions, a single-season NASCAR record that remains unbroken. He claimed his second Grand National Championship by a commanding margin. In 1956 he also won the International Stock Car Road Race, the first NASCAR Cup event held at Road America, a circuit that would not see stock car racing again until the 1990s.
Despite their combined success, Flock and Kiekhaefer had a contentious relationship. Flock departed the team immediately after a win at North Wilkesboro on April 8, 1956, citing stomach ulcers. He had compiled 21 victories in 46 starts with the team.
Away from the track, Flock was one of the more politically outspoken drivers of his generation. His support for a NASCAR drivers' union cost him dearly when NASCAR management disqualified and banned him, officially citing illegal carburetor modifications. The ban was widely understood to be retaliation for his union activities, a parallel to the treatment of fellow driver Curtis Turner. Flock continued racing under other sanctioning bodies — including the Midwest Association for Race Cars and USAC events — before being reinstated to NASCAR competition in 1966.
After his competitive years, Flock worked for Charlotte Motor Speedway in public relations and ticket sales and was employed by Ford Motor Company to entertain customers at track events. His final competitive appearance came in the 1991 Battle of NASCAR Legends at Charlotte Motor Speedway.
Flock died on March 31, 1998, from liver and throat cancer at age 73, during NASCAR's 50th anniversary season. NASCAR driver Darrell Waltrip honoured him with a special paint scheme at Darlington Raceway in the weeks before Flock's death, in part to help raise money for medical expenses Flock could not cover.
A month before his death, Flock was named one of NASCAR's 50 Greatest Drivers. He was inducted into the International Motorsports Hall of Fame in 1991, the National Motorsports Press Association Hall of Fame in 1972, and the NASCAR Hall of Fame in 2014. His single-season records from 1955 — 18 wins and 19 poles — remain benchmarks that define the ceiling of NASCAR's golden era.