Opperman came to wider notice in 1968 when Jerry Janssen, an employee of Speedway Motors, discovered him racing a sprint car powered by a Ranger airplane engine in California. Janssen brought him to Lincoln, Nebraska, which kickstarted Opperman's broader career. His unconventional background — running "outlaw" circuits rather than aligning with a single sanctioning body — gave him an exceptionally wide range of experience. He chased the best-paying races from track to track across the country, winning dozens of events each year.
His style and raw talent attracted the attention of established IndyCar veterans, including Parnelli Jones and A.J. Foyt. Opperman's personality during this period made him one of the more distinctive figures in American open-wheel racing: in his early years he was associated with the counterculture and drug culture of the 1960s, but while living in Beaver Crossing, Nebraska, he became a devout Christian and subsequently worked toward establishing a ranch in western Montana for troubled youth. One of his trademarks was a battered western hat that had belonged to his brother Jay, who died racing a sprint car at Knoxville Raceway on May 16, 1970.
Opperman won the 1971 Knoxville Nationals, the premier event in sprint car racing and one of the most prestigious dirt-track prizes in American motorsport. In 1976 he won the Hulman Classic at Terre Haute, Indiana, a race that drew most of the leading sprint car drivers in the country, including multiple drivers who would start the Indianapolis 500 later that same month.
Opperman made nine USAC Championship Car starts across the 1974 and 1976 seasons, including appearances at the 1974 and 1976 Indianapolis 500. His first start at Indianapolis came with a team co-owned by Parnelli Jones, himself a sprint car veteran and winner of the 1963 Indianapolis 500. Opperman recorded three top-ten finishes in his Champ Car outings.
Opperman was approaching the peak of his powers in the USAC sprint, midget, and Silver Crown divisions when disaster struck in early September 1976. He suffered critical head injuries while battling for the lead of the Hoosier Hundred at the Indianapolis State Fairgrounds. He missed the entire 1977 season recovering and returned to racing on the outlaw circuit in 1978, but never recaptured the level of form he had shown before the accident.
In 1981, Opperman was injured again in another racing accident that inflicted severe head injuries, leaving him disabled and requiring constant medical care for the remainder of his life. He died on September 4, 1997, in Fountain, Florida — sixteen years after that final career-ending crash at Jennerstown, Pennsylvania.
Opperman was inducted into the National Sprint Car Hall of Fame as a member of its inaugural class in 1990, a recognition of his stature among the foundational figures of the sport. In 2011 he was inducted into the International Motor Sports Hall of Fame in Talladega, Alabama.
Jan Opperman stands as one of the most compelling and ultimately tragic figures in American sprint car history. His natural talent was acknowledged by the sport's greatest drivers, and his wins at Knoxville and Terre Haute placed him among the elite of his era. That his career was cut short not once but twice by head injuries, long before the advent of modern safety equipment, gives his story an added weight that endures in the memory of the sport.