Greenberg got his start in film working in his uncle's second-hand camera store when he was thirteen. He eventually set up his own film and photography company, obtaining the exclusive rights to footage from 1967 International and Universal Exposition or Expo 67, as it was commonly known in Montreal. In 1973 he acquired Astral Communications and subsequently combined it with his own company "Ann Green Photos", named after his mother Ann Greenberg. Soon thereafter, it became one of the leading film production companies in Canada.