Similarly, Kelley's nickname is also derived from the sport. Another Johnny Kelley, "the Elder", was already an established marathon figure, having won Boston twice before "the Younger" became involved.

In the spring of 1957, the Younger Kelley ran a course-record 2:20.05 on the newly-measured route to win the storied Boston Marathon. On five additional occasions he was runner-up, while he placed in the top ten seven times, and was the first American finisher eight times. Overall, he has run the race 35 times.

Literally and figuratively, Kelley's running took him to great distances. In 1956 he travelled to Melbourne, Australia to represent the United States in the Summer Olympic Games. More accurately, Kelley represented Boston University. The three-man American marathon contingent was composed of Terrier teammates Kelley, Dean Thackwary, and Nick Costes.

Four years later, Kelley ventured to Rome, where he was the first American finisher in the 1960 Olympic Marathon. 

On the national scene, Kelley was an eight-time winner of the Yonkers Marathon (1956-63), which was annually designated as the AAU National Championship.

Although more interested in distance than track, Kelley enjoyed considerable success at Boston University. He established school records in the one and two-mile races, and won the IC4A and New England Cross-Country titles, before placing second at the 1953 NCAA Championships.

Elected into the Boston University Hall of Fame in 1959, Kelley was later inducted into the Helms Foundation Hall of Fame in 1967.