William Perry was born in Elmira, New York. He began composing and conducting in his teenage years, producing a full-length musical at the age of 16. This led to musical study at Harvard University where his teachers included Paul Hindemith, Walter Piston and Randall Thompson. While there, Perry organised his own symphony orchestra and chorus, specializing in 18th-century music. During post-graduate military service in Germany, Perry wrote a musical theatre piece called Xanadu that toured Europe for more than five years.

When the job of musical director and silent film accompanist at the Museum of Modern Art in New York became available, Perry was selected for the post and over the next twelve years composed more than a hundred film scores for such silent screen classics as The Gold Rush, The General, Orphans of the Storm, Blood and Sand and others. He is credited with playing a significant role in the revival of interest in films of the silent era, and his television series, The Silent Years, hosted by Orson Welles and Lillian Gish, won an Emmy Award and introduced silent film classics to two new generations of film-goers. He produced and composed the scores for the Peabody Awardwinning Mark Twain Series of feature films on PBS (1980–85), and his Broadway musical, Wind in the Willows, starring Nathan Lane, won him Tony nominations for both music and lyrics (1986).

Throughout his more recent career, Perry has alternated the writing of film and stage music with concert compositions. His music has been performed by the Chicago Symphony, the Saint Louis Symphony, the Detroit Symphony and the symphonic orchestras of Minnesota, Montreal, Calgary and Hartford as well as the Vienna Symphony, the Rome Philharmonic, the Slovak Philharmonic, the RTÉ National Symphony of Ireland and other orchestras in Europe. Perry has for many years resided in the Berkshires of Massachusetts, just a short drive from Tanglewood.