Aitken competed in the Indianapolis 500 three times. He started the race twice, in 1911 and 1916. He led the first lap of the first race (1911). Aitken captured the pole position in 1916, but ended up in 15th place (his best finish) that year. In the 1915 Indianapolis 500, Aitken drove relief for two drivers, Gil Anderson and Earl Cooper (who ultimately finished 3rd and 4th).