Neill was accepted into the USC Thornton School of Music as a flutist, but quickly turned to composition as his main focus, studying with composer Morten Lauridsen, among others.

Coursework at Harvard with notable ethnomusicologist Bruno Nettl led to a research grant to study Taarab music and Swahili culture in conjunction with the Institute of Kiswahili and Foreign Languages in Zanzibar, Tanzania.

While a student at Harvard, Neill received the BMI Pete Carpenter Fellowship in 1991, which provided him the means to re-locate to Los Angeles and begin his professional career.

Amazon subsequently released the soundtrack album for Mozart in the Jungle, which features Neill's orchestral reimagination of Phoenix's "Lisztomania", the series's main title.

[27] Like Father (2019), a film for Netflix starring Kristen Bell, Kelsey Grammer and Seth Rogen, features Neill's Hawaiian-style slack-key guitar playing.

Much of his ad work has been in collaboration with distinguished film directors, including Kathryn Bigelow, Roman Coppola, Mike Mills, Rupert Sanders, Gus Van Sant, and Angus Wall.

[30] Neill's controversial musical The Beastly Bombing or A Terrible Tale of Terrorists Tamed by the Tangle of True Love was written with librettist Julien Nitzberg and premiered in 2006.

[10] The Beastly Bombing drew comparison to Mel Brooks and was dubbed by The Huffington Post: "the first great work of comedy to emerge from the post-9/11 little planet of horrors."

Alongside composer Larry Groupé, Neill is co-founder of the Palomar Film Music Workshop which meets yearly in the Pauma Valley in San Diego County.