Horner was educated at London's Royal College of Music, the University of Southern California (bachelor's degree) and the University of California at Los Angeles (masters & doctorate), and began his scoring career working for prolific B-Movie director and producer Roger Corman. He then went on to compose sountracks for a variety of well-known movies, including 48 Hours, Star Trek II: The Wrath of Khan, Aliens, Field of Dreams, Braveheart, and Apollo 13.

His most famous work is for the film Titanic, for which he received Academy Awards for Best Original Dramatic Score and Best Original Song for "My Heart Will Go On", which he co-wrote with Will Jennings. His work on Titanic also won three Grammy Awards, two Golden Globe Awards, and went on to become the best-selling film sountrack in history up to that point, with over 24 million copies sold worldwide.

Film scores

• House of Sand and Fog (Academy Award Nomination, best Original Score)
• The Missing
• Windtalkers
• A Beautiful Mind (Oscar, Grammy, and Golden Globe nominations)
• Enemy at the Gates
• Dr. Seuss' How the Grinch Stole Christmas
• The Perfect Storm
• Titanic (4 Grammys, 2 Oscars, 2 Golden Globe awards)
• Courage Under Fire
• Jumanji
• Apollo 13 (Oscar nomination)
• Braveheart (Oscar & Golden Globe nominations)
• Legends of the Fall (Golden Globe nomination)
• The Pagemaster (Oscar nomination)
• The Pelican Brief
• Swing Kids
• Sneakers
• The Rocketeer
• An American Tail II
• Another 48 Hours
• I Love You To Death
• Glory (Grammy Award, Golden Globe nomination)
• Field of Dreams (Oscar nomination, 2 Grammy nominations)
• Honey, I Shrunk The Kids
• Cocoon II
• Willow
• Aliens (Oscar nomination)
• An American Tail (Oscar nomination, 2 Grammy awards, Golden Globe nomination)
• Cocoon
• Star Trek III: The Search For Spock
• 48 Hours
• Krull
• Star Trek II: The Wrath of Khan
• Wolfen
• The Hand
• Battle Beyond the Stars
• Captain Eo