Born in Somerville, Massachusetts, Hepburn's family moved to Los Angeles, California when he was ten years old. He began riding motorcycles as a teen and his skills led to him signing on with a cycle performing group in 1914 that toured the West Coast and parts of the American Midwest. He then began competing in on board tracks, then on dirt. His racing career was interrupted during 1917 and 1918 due to World War I.
In June 1919, Hepburn came to national prominence when he won the 200 mi (320 km) National Championship at Legion Ascot Speedway in Los Angeles riding for the Harley-Davidson factory. He began winning consistently thereafter and in 1921 won the "Dodge City 300 National Championship" while breaking all existing 300 mi (480 km) records. In 1922 he dominated professional track racing for the Indian Motocycle company. That year, he rode to his second victory in the 300 mi (480 km) National Championship motorcycle race, this time at Meridian Speedway in Wichita, Kansas.
In 1925, he competed in a car built by Harry Miller in the first of fifteen appearances at the Indianapolis 500. Later that year, during practice for the AMA 100-mile (160 km) championship race at Altoona, he crashed his Harley-Davidson racing motorcycle and damaged his hand. Hepburn then lent the motorcycle to Indian rider Joe Petrali, who won the race and shared the prize money with him. This began Petrali's association with Harley-Davidson.
In 1929 he qualified third at Indianapolis, but gear problems resulted in him having to drop out after only fourteen laps. He finished third in 1931, and although he led the famous race three times in three different decades and had four finishes in the top five, his best result came in 1937 with a second place finish 2.16 seconds behind Wilbur Shaw, the closest ever at that time.
For a time, Hepburn served as president of the American Society of Professional Automobile Racers. In 1946, at the age of fifty, Hepburn qualified Novi Governor Special at of 134.449 mph (216.375 km/h). He led forty-four laps in the race before the car stalled on Lap 121.
In 1947, Hepburn joined Preston Tucker and Tucker Corporation and drove the prototype Tucker onstage when it was unveiled to the public on June 19, 1947. He served as West Coast Regional Manager for Tucker Corporation.
Ralph Hepburn died during qualifying practice for the 1948 Indianapolis 500 while driving for Tucker Corporation. He was survived by his wife Ida Mae Hepburn and one daughter Joanne Hepburn. He was buried at Forest Lawn Memorial Park Cemetery in Glendale, California.
 Indy 500 results
|Wikimedia Commons has media related to: Ralph Hepburn|