Englishby was born in Preston, Lancashire in 1970. He was musically active by his teenage years, performing as a Pianist in big bands and jazz ensembles as well as writing and composing his own works. He studied at Goldsmiths' College and at the Royal Academy of Music, where he received the Charles Lucas Prize for Composition and the Arthur Hervey Scholarship, as well as receiving a BBC Sound on Film Commission. The Last Clarinet for orchestra and narrator was Englishby's first published work, and continues to be performed internationally. His other works include Short Symphony (1997), String Quartet (1995) and Blackpool Lights for Orchestra (1993). Aside from these Englishby composed pieces for his own group, The Paul Englishby Big Band, which has performed at Ronnie Scott's Jazz Club.

As well as commissions for film and TV, he has composed classical works for various ensembles. His credits include The Last Clarinet for solo clarinet, orchestra and narrator in 1995, Byron for large orchestra and Weep No More for string orchestra. Englishby also recently completed a large public arts commission entitled Fireworks, several pieces for choir, orchestra, chamber group and school children, in commemoration of the Combe Down Stone Mines Project in Bath.

As orchestrator, Conductor and Pianist, Englishby has worked with The London Orchestra, Britten Sinfonia, London Musici, Tallis Chamber Choir, Fibonacci Sequence and BBC Concert Orchestra to name a few. He has conducted on studio sessions and film scores both in the UK and abroad, as well as on recordings and broadcasts for radio and television. Credits include Richard Eyre's The Other Man and Michael Radford's Flawless in 2008. He worked on the Universal movie Your Highness, starring Natalie Portman and James Franco, released in 2011. Englishby orchestrated and conducted Tony Banks's classical album Six: Pieces for Orchestra, released in 2012.

He won the ASCAP Award in 2009 for his film score to Miss Pettigrew Lives for a Day, directed by Bharat Nalluri. He also wrote the score for Lone Scherfig's Oscar nominated feature An Education, starring Carey Mulligan, and A Royal Night Out, starring Rupert Everett and Bel Powley. He was also music Director and Composer for the 2013 film Sunshine On Leith, featuring songs by The Proclaimers, and directed by Dexter Fletcher. Englishby has collaborated with world-class film Directors, including Debbie Isitt on critically acclaimed Brit-flick Confetti, and on the film Ten Minutes Older featuring works from Directors Spike Lee, Werner Herzog, Bernardo Bertolucci, Mike Figgis and Jean-Luc Godard.

In recent years, Englishby has written the original scores for a number of films and television programmes. In 2012 he won the Emmy Award for Best Original Main Title Theme Music for Page Eight, starring Bill Nighy and Rachel Weisz. He also received an Ivor Novello nomination.

In 2013, Englishby scored Peter Morgan's The Audience, starring Helen Mirren as Queen Elizabeth II. The Audience, with Mirren, transferred to Broadway in 2015, with Kristin Scott Thomas taking up the role in the West End. In 2014, Englishby wrote the music for David Hare's Skylight, starring Bill Nighy and Carey Mulligan, which also transferred to Broadway from the West End in 2015.

Other notable credits include Red Velvet, starring Adrian Lester, which played at the Garrick Theatre in early 2016, Hedda Gabler, starring Sheridan Smith at the Old Vic, and Emil And The Detectives at the National Theatre.