Yunick was born to Ukrainian immigrant parents and grew up on a farm in Neshaminy Falls, Pennsylvania. His father's death forced him to leave school at 16 to run the farm, a circumstance that sharpened his practical engineering instincts — he constructed a working tractor from the remains of a scrapped car. In his spare time he built and raced motorcycles, acquiring the nickname "Smokey" from the exhaust habits of one of his machines.
During World War II, Yunick served with the United States Army Air Corps. Military records reflect that he was drafted as a welder in January 1943 and served on active duty until March 1946, during which time he received an Air Medal from the 15th Air Force. In 1946 he married and moved to Daytona Beach, Florida, drawn by memories of flying over it on training missions.
In 1947, Yunick opened "Smokey's Best Damn Garage in Town" at 957 N Beach St. in Daytona Beach, initially repairing trucks. He operated the garage until 1987, when he closed it on his own terms. The property was sold after his death according to his estate plan, and most of the buildings were eventually demolished.
Yunick's entry into stock car racing came through Marshall Teague, a local team owner who recruited him despite Yunick having no prior knowledge of the sport. He prepared a Hudson Hornet for driver Herb Thomas for the second running of the Southern 500 at Darlington, and it won the race. That result established his reputation, and it never faded.
As Chevrolet's unofficial factory race team, Yunick became deeply embedded in the development of the Chevrolet small-block engine; much of the engine's high-performance evolution ran through his shop in some form. He raced Chevrolets in 1955 and 1956, switched to Fords in 1957 and 1958, and then ran Pontiacs from 1959 through 1963. With Pontiac, he became the first team owner to win the Daytona 500 twice — in 1961 and 1962. He was also the first to put a driver on the Daytona 500 pole three consecutive times, achieving this with Fireball Roberts in 1960, 1961, and 1962.
Between 1958 and 1973, Yunick also competed at the Indianapolis 500. His car won the 1960 race, and he produced several memorable experimental designs, including the 1959 "Reverse Torque Special" with the engine running in reversed rotation and the 1964 "Hurst Floor Shifter Special" with the driver's capsule mounted as a sidecar. In 1962 he mounted a downforce wing on Jim Rathmann's Watson Roadster — an innovation that USAC immediately banned, though wings later became standard across Can-Am and Formula One.
Yunick was famous for operating at — and often beyond — the boundary of what the rules permitted. His most celebrated case was the 1966 Chevrolet Chevelle driven by Curtis Turner, which was dramatically faster than any rival. Investigation eventually revealed that Yunick had lowered the roof and windows while raising the floor, altering the body profile while keeping it apparently stock. NASCAR subsequently required templates to verify the exact production dimensions of each car's roof, hood, and trunk.
Another widely repeated story holds that Yunick once had nine items flagged by NASCAR officials before a car could race. When inspectors removed the fuel tank for examination, Yunick reportedly started the car without a tank and drove it back to the garage, saying, "Better make it ten." The fuel tank incident has since been disputed.
His engineering creativity extended beyond rules bending. He developed air jacks for stock cars in 1961 and designed an early safe-wall barrier system for racetracks in the early 1980s using tires between sheets of plywood; neither innovation was adopted by NASCAR at the time. He also built and tested a 1968 Camaro for Trans-Am racing with an extensive set of weight-saving and aerodynamic modifications including acid-dipped body panels and a widened front end.
After Fireball Roberts died in 1964 from burns sustained in a crash at Charlotte, Yunick campaigned persistently for safety reforms. Repeatedly overruled by NASCAR's Bill France Sr., he left the sport entirely in 1970.
From the 1980s onward Yunick wrote a technical column, "Track Tech," for Circle Track magazine and contributed an occasional "Say, Smokey..." column to Popular Science. He held at least nine US patents. In 2001, shortly before his death, he published his autobiography Best Damn Garage in Town...The World According to Smokey.
Yunick was inducted into the International Motorsports Hall of Fame in 1990 in its inaugural year, and into the Motorsports Hall of Fame of America in 2000. He is a member of more than 30 Halls of Fame across the United States and internationally.
After his death, his garage's full contents — cars, engines, tools, and parts — were auctioned off as he had requested, the proceeds going to a foundation supporting motorsport innovation. A marker was erected at Smokey Yunick Way in Holly Hill, Florida, alongside the former garage property. The character Smokey in the 2017 Disney/Pixar film Cars 3 is modelled on Yunick, voiced by Chris Cooper.