Quast was born in 1957 in Tamworth, New South Wales, Australia, but currently lives in Great Britain.He is married with three children. Quast also teaches at the National Institute of Dramatic Art in Sydney, Australia.

Quast played the part of Javert in Les Miserables in Great Britain and Australia, as well as in Les Misérables - The Dream Cast in Concert at the Royal Albert Hall, on the Les Misérables Complete Symphonic Recording, and in Hey, Mr. Producer, a concert in honour of Sir Cameron Mackintosh. He has thrice won the Laurence Olivier Award for Best Actor in a Musical:

Quast co-starred in the musical version of The Secret Garden (musical) opposite another famous Australian actor, Anthony Warlow. Though mainly a baritone, Quast has played some roles written for tenors, namely George (see above), Candide, and Archibald Craven in The Secret Garden. Although he is known for his serious roles, he has also performed comedic parts, such as his 2004 appearance as the pompous Miles Gloriosus in a limited run revival of A Funny Thing Happened on the Way to the Forum at the Royal National Theatre.

Philip Quast more recently played the supporting role of Juan Peron in Andrew Lloyd Webber's 2006 production of Evita at the Adelphi Theatre in London. He was nominated for but did not win an Olivier award for this role.

In July 2007, Quast performed the role of Judge Turpin in a concert version of Sweeney Todd at London's Royal Festival Hall.

Quast was most recently in the Menier Chocolate Factory production of Jerry Herman's La Cage aux Folles as Georges.

Quast rejoined the cast of La Cage Aux Folles on May 4 2009 with Roger Allam. Coincidentally, both actors have performed in the role of Javert in Les Miserables

From July 2010, Quast will play Mr Banks in the Australian premiere production of Mary Poppins at Melbourne's Her Majesty's Theatre.

Philip Quast has appeared in the cast recordings for many musicals, but has also released his own album, Live at the Donmar, containing both covers and original material.

Quast has also made numerous appearances on television and the big screen. Major roles include: