Thomas Pasatieri (born New York, United States, October 20, 1945) is an American opera composer.
He began composing at age 10 and, as a teenager, studied with Nadia Boulanger. He entered the Juilliard School at age 16 and eventually became the school's first recipient of a doctoral degree.

Pasatieri has taught composition at the Juilliard School, the Manhattan School of Music, and the Cincinnati College-Conservatory of Music. From 1980 through 1984, he held the post of Artistic Director at Atlanta Opera.

He has composed 24 operas, the best known of which is The Seagull, composed in 1972. Two of his operas were premiered in 2007: Frau Margot by the Fort Worth Opera and The Hotel Casablanca in San Francisco. Other popular operas include La Divina and Signor Deluso.

In 1984, Pasatieri moved to Los Angeles, California, where he formed his film music production company, Topaz Productions. His film orchestrations can be heard in Billy Bathgate, Road to Perdition, American Beauty, The Little Mermaid, The Shawshank Redemption, Fried Green Tomatoes, Legends of the Fall, Thomas Newman's Angels in America and Scent of a Woman, among many others. In 2003, Pasatieri returned to New York to continue his concert and opera career.