Hillier was born in Dorchester, England in 1949, where he attended Hardye's Grammar School. In 1967 he became a music student at the Guildhall School of Music & Drama, studying voice.

In 1974 he co-founded the Hilliard Ensemble along with fellow vicar-choral Paul Elliott, tenor, and counter-tenor David James. His concert debut was in 1974 in London's Purcell Room.^[1] Hillier remained the director of the ensemble until 1990, when he founded Theatre of Voices. In addition to early music, this group explores more contemporary repertoire. With the Chicago-based ensemble His Majestie's Clerkes Hillier recorded early American repertoire such as the works of William Billings on the 1992 album A Land of Pure Delight.^[1]

Hillier later became Director of the Early Music Institute at the Indiana University Jacobs School of Music where he conducted the Pro Arte Singers. He left the E.M.I. in 2003, having meanwhile become Artistic Director and Principal Conductor of the Estonian Philharmonic Chamber Choir;^[2] he left the position in 2007.^[3]

Since 2003, Hillier has made his home in Copenhagen, where he is Chief Conductor of Theatre of Voices (1990-) and Ars Nova (Copenhagen) (2003-2023). In 2008, he was appointed Artistic Director and Chief Conductor of the National Chamber Choir of Ireland.^[3]

He continues to work with his own group, Theatre of Voices. THEATRE OF VOICES is an internationally recognized Danish vocal group which has close to 40 releases and several awards, including a Grammy and P2 awards. Theatre of Voices’ repertoire covers a wide range of genres and stretches from the earliest notated music to modern sound art installations and contemporary opera. The group was founded in London in 1990 by Paul Hillier and is considered one of the world's leading vocal ensembles. After some years in the USA, Hillier moved back to Europe in 2004 to settle in Denmark, where the ensemble is now based. In 2013, the group was nominated for the Nordic Council Music Prize. This inspired commissioning of even more Nordic repertoire and resulted in a North Atlantic Tour in 2019 that included works from Greenland, Iceland, Faroe Islands, Denmark and Estonia featured on both concerts and local workshops.

Hillier has recorded a number of solo albums, some with harpist Andrew Lawrence-King on the Harmonia Mundi, ECM, EMI, Finlandia and Hyperion labels.

From 1980, Hillier has held a variety of academic appointments over the years, most recently as Director of the Early Music Institute at Indiana University Bloomington.^[1][4]

• The Catch Book (1987), Oxford University Press, ISBN 0-19-343649-3, a collection of catches (comic rounds) edited by Hillier.
• A Josquin Anthology (2005), Oxford University Press, ISBN 0-19-353218-2, a collection of choral pieces by Renaissance composer Josquin des Prez, edited by Ross Duffin and Hillier.
• Writing on Music, 1965–2000 (2002), Oxford University Press, ISBN 0-19-511171-0, a collection of writings by composer Steve Reich, edited by Hillier.
• Arvo Pärt (1997), Oxford University Press, ISBN 0-19-816616-8, The first English-language study (including a short biography) of Estonian composer Arvo Pärt.
• English Romantic Partsongs (1986), Oxford University Press, ISBN 0-19-343650-7, a collection of songs edited by Hillier.
• 300 Years of English Partsongs: Glees, Rounds, Catches, Partsongs 1600-1900 (1983), Faber & Faber, ISBN 0-571-10045-7, a collection of music edited by Hillier.

• Paul Hillier on Bach-Cantatas
• Paul Hillier on Harmonia Mundi
• Classical Archives interview at the Wayback Machine (archived 12 October 2012)