Scully hooked up with the band in 1965 just after they changed their name from the Warlocks and was instrumental in their rise. He organised their original record deals, planned their early tours and famously demanded that Woodstock organisers pay the group up front ahead of their 1969 performance. In 1968 he masterminded a plan to smuggle the group through a group of striking students who had shut down the Columbia University campus for a show.

He was fired from his position by the band in 1984 because of his addiction to morphine and cocaine but returned to the fold in 1985. Grateful Dead guitarist Bob Weir paid tribute to Scully saying he was a huge part of their success and stated that together they "made history."