Kelly attended Wellington Mepham High School in Bellmore, New York. On graduation in 1946 he received a five-year engineering scholarship from Grumman Aircraft. He joined Grumman as a propulsion engineer after graduating from Cornell University in 1951 and married his wife Joan in 1952. He was called for two years of duty in the US Air Force in 1956. After his discharge he returned to Grumman, where he worked for the rest of his life.
In 1960-1972 he managed design, development, and flight of the Apollo Lunar Module. For this he received NASA's Distinguished Public Service Medal in 1972. Thereafter he was deputy director for Grumman's space shuttle proposal. After the loss of that program to Rockwell, he served in various Grumman corporate positions, ending his career as President of the Space Station Integration Division in Reston, Virgina. He retired from Grumman in December 1992.
He published an autobiography, Moon Lander: How We Developed the Apollo Lunar Module in May 2001.
Birth Place: Brooklyn, New York.