Cy Marshall was born in Kansas City, Missouri. He first drove in the Indy 500 in 1928 as relief for Earl DeVore.
He was hurt badly in the 1930 Indy 500 when his Duesenberg Special crashed through the northeast wall on lap 29 at over 100 mph and went over the banking. His brother Paul, who was his riding mechanic, was trapped under the car and died. Cy was thrown out and suffered a broken jaw and other injuries. Despite this tragedy, Cy carried on racing.
He raced in the Indy 500 again in 1947 after a wait of 17 years, finishing 8th in the Tattersfield Special A.R.Weil/Alfa Romeo. He returned to the Brickyard once more in 1950 but failed to qualify.
He became a mechanic and continued racing into his 50s.