Green passed the Pennsylvania bar exam in 1951, achieving the highest score in the state. Green's early mentors included Robert N.C. Nix, Sr., who lived across the street from Green's family. In January 1952, after being admitted to the bar, Green took over the practice of Thomas Reed, a black Philadelphia lawyer who was joining the Philadelphia District Attorney's Office under Richardson Dilworth (Green had also interviewed at the DA's office, but decided that he "couldn't fit in as a prosecutor").