Lewis grew up in Lakewood, Ohio and attended Lakewood High School. He played football and baseball, and was on a Lakewood basketball team that reached the state high school championship game in 1941. Lakewood's football team tied for the Lake Erie League championship in 1940 and 1941, when Lewis played left halfback. Lewis later transferred to Staunton Military Academy in Virginia, and in 1942 set a school scoring record in football with 14 touchdowns and 282 total points.
Lewis entered the U.S. Navy in 1945 and was a triple threat player and alternate quarterback for the Fleet City, California Bluejackets, a military team. The Bluejackets won the national service title that year.
The Los Angeles Rams of the National Football League (NFL) selected Lewis with the 200th pick in the 1946 NFL Draft, but NFL commissioner Bert Bell ruled him ineligible under league rules. The Rams took Lewis thinking he was in the 1946 graduating class, but he had one more year of eligibility left as an athlete who entered college in 1943. The decision delayed Lewis's professional career for a year; in 1946 he signed with the Cleveland Browns of the new All-America Football Conference (AAFC). Lewis started at quarterback for the Browns in their first three games in his first season, sharing duties with Otto Graham. After Graham took over as the starting quarterback, he became a defensive back who also returned punts and kickoffs. Lewis had five interceptions in his first season, when the Browns won the AAFC championship. Cleveland won the league championship in each of the ensuing three years before the AAFC dissolved and the Browns were absorbed into the more established NFL.
The Browns beat the Rams to win the NFL championship in 1950, the team's first year in the league. The following year, Lewis returned a Bob Waterfield interception for 12 yards to the Cleveland 32-yard line during the Browns' 24–17 loss to the Rams in the NFL title game at the Los Angeles Coliseum. After the 1951 season, Lewis retired from the Browns to devote himself full-time to his insurance business.
^"Penn Easily Beats Princeton, 66 to 52". The New York Times. February 11, 1945. p. 51.
^"Triple-Threat Star". Los Angeles Times. December 4, 1945. p. A8.
^"The Hyland Fling". Los Angeles Times. December 4, 1945. p. A8.
^ ab"Mutryn, Kolesar and Cliff Lewis Are Signed by Cleveland Browns". Cleveland Plain Dealer. February 19, 1946. p. 18. Lewis, 22, is a product of Lakewood High, and at Duke was an outstanding back who sparked the Blue Devils' 29-to-26 victory over Alabama in the 1945 Sugar Bowl game at New Orleans. Last season, in the Navy, he was a member of the crack Fleet City (Cal.) Bluejackets who won the national service title.
^"Rams Lose Two Draftees". Los Angeles Times. May 28, 1946. p. A7.