In 1954 Keller began a transition to Championship Cars. He drove in the AAA and USAC Champ Car series, racing in the 1954-1959 and 1961 seasons with 32 starts, including the Indianapolis 500 six times. He was involved in the crash that killed Bill Vukovich in 1955. He finished in the top ten 13 times, with a best finish of 2nd two times (Atlanta in 1956, and Milwaukee in 1961). His best Indy 500 finish was 5th in 1961.