He began his racing career in 1908 in San Fransisco in a borrowed car. He won the race, but lost his job as a mechanic after he beat one of his bosses, so he became a full-time racer. He joined the Stutz team in 1912. In 1913 he won seven of eight major races (and finished second in the other), and won the |AAA national championship. He was injured for the 1914 season. He missed the first several months of the 1915 season, but won the AAA championship anyhow. Cooper got another late start in 1916 after Stutz pulled out of racing, and he finished fifth in the championship. The won the World War I shortened 1917 season, and then he retired.
Cooper raced in the 1919 Indianapolis 500.
Cooper returned to replace Joe Thomas who broke his arm in October 1921, and won a 200 mile race at Fresno. He returned to racing full-time in 1922, and won five races in 1923.
Cooper raced in the 1924 Indianapolis 500, and was leading after 400 miles. A tire blew, and he had to pit. He returned second, and worked his way back to the lead with 30 miles left in the race. He blew another tire just as he was passing Joe Boyer, and the pit stop forced him to settle for second. He started at Indy in 1925, and won the pole in his final Indy 500 in 1926. He retired for good in 1928.
He was inducted in the Motorsports Hall of Fame of America in 2001.