After a year studying at University of California, Berkeley with Joseph Kerman, he returned to Cambridge as a Fellow of King's College and completed his PhD there in 1965.

[2][3] He was appointed Associate Dean of Humanities, Arts, and Social Sciences at Riverside in 1998, a position which he held until 2001 when he became Distinguished Professor of Musicology at University of California, Los Angeles.

On the sixth anniversary of his death, the University of California, Riverside dedicated the Philip Brett Memorial Peace Garden, a traditional Japanese Karesansui designed by Takeo Uesugi.

[8] On Dart's recommendation, Brett was appointed General Editor of the new seventeen-volume Byrd Edition, which revised (and in some cases replaced) the work begun by Fellowes.

According to Anthony Bye writing in The Musical Times, it was to become the first modern multi-volume, critical edition of a major English composer to reach completion.

In 1976, Brett delivered a paper on Benjamin Britten's opera Peter Grimes at a national meeting of the American Musicological Society.

"[9] The reaction was mixed, and when Brett initially submitted the paper to The Musical Quarterly for publication, the then editor, Joan Peyser, dismissed it as "a personality study".

In the succeeding years he wrote a series of influential articles and books both on Britten and on the more general implications of gay and lesbian sexuality in music.

As a choral conductor, he received the American Musicological Society's Noah Greenberg Award in 1980 for the performances of Jacopo Peri's Euridice and Monteverdi's Orfeo as well as motets from Byrd's Gradualia.