Starting at age six, she took piano lessons, and by her teens was composing her own pop songs. After high school, Lewis earned her music degree from the Welsh College of Music and Drama, where she had majored in classical composition for piano and flute. Upon graduating, she spent a year teaching music in Sussex, after which she moved to Birmingham to hone her skills, playing solo piano shows and with local bar bands. By 1990, Lewis had developed a loyal fan base and begun recording demos of her songs in her home studio. A demo of "I Love You Always Forever" caught the ear of Atlantic Records chairman Doug Morris, who purportedly flew Lewis to New York for an audition and quickly signed her to the label.

In 1996, she released her debut album, Now in a Minute, which featured production from Kevin Killen (David Bowie, Peter Gabriel, Shawn Colvin) and included the single "I Love You Always Forever." An infectious, buoyant production reminiscent of the poppier end of Kate Bush's sound, "I Love You Always Forever" was a breakthrough hit for Lewis, staying at the number two spot on Billboard's Hot 100 chart for nine consecutive weeks and ultimately reaching platinum status. The song's popularity was a boon to Lewis, who next appeared as herself on an episode of the FOX television drama Beverly Hills, 90210, and dueted with Richard Marx on the song "At the Beginning" for the soundtrack to the 1997 animated film Anastasia.

Lewis returned in 1998 with her sophomore album, the Killen-produced Blue Planet. While the album was well-received, generating the number one Billboard dance chart single "Love Him," as well as the lesser European chart hit "I Could Be the One," it failed to match the outsized success of Now in a Minute, and Lewis eventually parted ways with Atlantic. Switching gears, she collaborated with guitarist/producer David Torn on the electronica EP Chute, and moved to a more stripped-down acoustic sound for her third album, 2002's independently produced Be Still.

Over the next several years, Lewis stayed busy writing and recording material for her follow-up; a process that was put on hold for two years when she gave birth to her daughter. In 2008, she released her fourth album, In the Pink, which found her returning to the lush, electronic-tinged pop of her debut.

In 2015, Lewis delivered the jazz-inflected covers album Brand New Day, which featured her vocals backed by iconoclastic trio the Bad Plus. Along with stripped-interpretations of songs by David Bowie, Chocolate Genius, and others, the album also included the new composition "Sleep," and a reworking of "I Love You Always Forever." ~ Matt Collar