Born in Glasgow, Scotland in 1959, Armstrong studied music composition along with piano and violin at the Royal Academy of Music in London. After graduating in 1981, he won the Arts Council GLAA Young Jazz Musician of the Year honor in 1982. He toured with Ultravox's Midge Ure in 1985 and played piano on Ure recordings including 1988's Answers to Nothing. In 1988, he also composed the music for the Scottish Television miniseries Winners and Losers.
Continuing to juggle projects in different media in the '90s, he wrote music for multiple productions by the Royal Shakespeare Company beginning in 1994, the year that saw the release of the Massive Attack album Protection. It featured arrangements, conducting, songwriting, and piano by Armstrong. That year, he also completed a work for strings called Slow Movement. Back on television, he wrote score music for several 1996 episodes of the drama London Bridge.
In 1998, Massive Attack's Melankolic label released Armstrong's solo debut, The Space Between Us. In addition to a reworking of the song "Weather Storm" from their album Protection, it included the participation of guests including Cocteau Twins' Elizabeth Fraser and the Blue Nile's Paul Buchanan. He also made his feature-film debut as main composer on 1998's Orphans. That same year, Armstrong's string arrangements could be heard on Madonna's album Ray of Light. By the end of the '90s, he had also collaborated with such marquee acts as U2, Hole, the Spice Girls, the London Suede, and Tina Turner, in addition to many other artists. His continued work on the big screen included the 1999 Denzel Washington vehicle The Bone Collector, based on the best-selling novel.
With demand for his film scores increasing, Armstrong reunited with Luhrmann for the 2001 hit film musical Moulin Rouge. He won both the BAFTA and the Golden Globe for best score for his work on the movie. His second solo album, As If to Nothing, arrived on Melankolic in 2002. Its featured guests included Bono, the Lemonheads' Evan Dando, atmospheric rockers Mogwai, and electronic artist Photek, among others. Following his scores for 2002's The Quiet American and 2003's Love, Actually, he was nominated for another BAFTA for 2004's Ray, which won the Grammy for Best Score Soundtrack Album for Motion Picture, Television or Other Visual Media.
Armstrong's 2004 solo-piano album Piano Works consisted of pieces from his various soundtracks. A year later, he issued The Dolls, an experimental electronic collaboration with vocalist/producer Antye Greie and percussionist/producer Vladislav Delay. Still busy writing scores, he composed music for movies including 2005's Must Love Dogs, 2006's World Trade Center, and 2007's Elizabeth: The Golden Age. In 2008, he penned the score for the Marvel blockbuster The Incredible Hulk and issued his fourth solo album, Memory Takes My Hand. A classical release for EMI Classics, it featured a violin concerto for Clio Gould of the Royal Philharmonic Orchestra. In 2010, Armstrong was honored with an OBE appointment for his contributions to music.
His film scores in 2010 included the Oliver Stone sequel Wall Street: Money Never Sleeps and the teen drama Neds. Armstrong's first opera, The Lady from the Sea, premiered at the Edinburgh International Festival in 2012. His score soundtrack for Baz Luhrmann's lavish 2013 film version of The Great Gatsby was recognized with a second Grammy nomination. Consisting of 17 tracks, 11 of which were instrumentals, his 2014 solo outing, It's Nearly Tomorrow, featured returning guests such as Paul Buchanan and Vladislav Delay alongside celebrated trumpeter Chris Botti.
The year 2015 delivered the Armstrong film scores Far from the Madding Crowd and Victor Frankenstein. The biopic Snowden and the romantic comedy Bridget Jones' Baby hit screens with his music the next year. In 2018, he released a set of 16 minimalist compositions under the title Sun on You. It featured Armstrong on piano, backed by the Scottish Ensemble. He returned to theaters in 2019 with three features: Mrs. Lowry Son, The Burnt Orange Heresy (co-starring Mick Jagger), and Dirt Music, an adaptation of the Tim Winton novel. Another literary adaptation, The One and Only Ivan, based on the Newbery Medal-winning children's novel, followed in 2020. Next for Armstrong was the C.S. Lewis biopic The Most Reluctant Convert, which saw release in 2021. That year also brought the Modern Recordings release of his Nocturnes: Music for 2 Pianos, which he composed in 2020 and early 2021.~ Marcy Donelson, Rovi