Roberts was born on 12 February 1900 in Jamestown, North Dakota, the son of Frederick Augustus Roberts and Ruby Lenore Roberts. Around 1920 the family relocated to California. By 1924, Roberts was already building a reputation in auto racing circles on the West Coast, competing at Ascot Speedway in California and participating in a series of races in Hawaii. He married Edna Vincent in September 1925.
Roberts raced across American oval circuits for two decades before reaching the Indianapolis 500's victory lane. His path was long — 22 years of racing — without a major championship win, which gave his 1938 victory a particular resonance.
Roberts entered the 1938 Indianapolis 500 in the Burd Piston Ring Special, entered by car owner Lou Moore. He won the pole position with a qualifying speed of 125.681 mph, setting a new record at the time.
During the race, Roberts drove a gasoline-powered car, putting him at a fuel-consumption disadvantage against the alcohol-fuelled machines that had dominated qualifying. As those rival cars were forced to pit earlier and more frequently for refuelling, Roberts moved to the front. He made his sole pit stop — for fuel and a tyre change — at around 300 miles, briefly surrendering the lead to Jimmy Snyder. When Snyder's alcohol-fuelled car required a third fuel stop 75 miles later, Roberts regained the lead for good. He finished with a record average speed of over 117 mph and prize winnings totalling more than $32,000. Before the race, Roberts had reflected on his long career without a major win: "My luck has always run in cycles. Now it's running good and I'll win." Car owner Moore noted that Roberts had long spoken of retiring to a farm once he had saved enough money.
Roberts returned to defend his title in 1939 driving the same car that had brought him victory the year before. On lap 106, Bob Swanson's car lost control and went sideways. Roberts' car struck Swanson's, sending Roberts' machine over the outer wall, through a fence at approximately 100 mph, and headfirst into a tree. Swanson's car overturned and caught fire. Chet Miller, attempting to avoid the wreck, swerved into the debris and his car flipped against the inner wall. Roberts, Swanson, and Miller were all transported to hospital; two spectators were also injured by flying debris.
It took over 30 minutes to clear the burning wreckage of Swanson's car from the track. Roberts died later that day at Methodist Hospital from a broken neck among other injuries. His death was announced before the race concluded. Reports at the time noted that Roberts had intended for the 1939 race to be his last before retirement.
Roberts was the first defending Indianapolis 500 champion to be killed in competition at the event, a distinction that set a grim marker in the race's history.
Roberts was inducted into the Auto Racing Hall of Fame in 1985. His 1938 victory stands as one of the race's notable stories of perseverance — a career-long journey to the top step that ended with only one season as champion.