Gabrielle Cavassa was born on July 5, 1994, in Escondido, California, into a family of Italian descent, and grew up with an extended Italian family and time spent abroad that left her with a lasting taste for Italian pop and cabaret, above all the singer Ornella Vanoni. She began collecting records as a child and listening to them obsessively, among them albums by Nina Simone, Billie Holiday, Phyllis Hyman, Ella Fitzgerald and Nancy Wilson. She took piano lessons from the age of ten, but as a singer she is largely self-taught. After high school she studied at San Francisco State University, where she earned a Bachelor of Arts in Music; she has said her real schooling came from playing and sitting in at San Francisco jazz clubs during those years. In 2012 she was a contestant on the eleventh season of American Idol, going as far as the Hollywood rounds.

In 2017, after a visit, she moved to New Orleans and quickly joined the local scene, touring with drummer Adonis Rose and the New Orleans Jazz Orchestra and with trumpeter Irvin Mayfield, and getting to know the drummer and singer Jamison Ross and the veteran vocalist Germaine Bazzle, who became an influence. In 2018 she was a finalist in the International Sarah Vaughan Jazz Vocal Competition, held in conjunction with the James Moody Jazz Festival in Newark. Her debut album, Gabrielle Cavassa, came out on August 21, 2020. Ross and Cavassa produced it with a band of pianist Ryan Hanseler, bassist Lex Warshawsky and Ross on drums, plus guests saxophonist Braxton Cook, trumpeter Ashlin Parker and guitarist Ari Teitel; it mixes originals with a tribute to Bazzle ("To You My Love") and the standard "I Want to Talk About You."

On June 6, 2021, at the New Jersey Performing Arts Center, she shared first prize in the delayed 2020 Sarah Vaughan competition with Los Angeles singer Tawanda Seussbrich-Joaquim, the first time in the contest's nine-year history that two winners were named. Her profile rose further when Joshua Redman's manager heard her sing at a wedding in New Orleans and Redman invited her to sing on where are we (Blue Note, September 15, 2023), recorded at Esplanade Studios in New Orleans, his first album to feature a vocalist and his first as a Blue Note artist. DownBeat gave it five stars and called her "a star in the making." From fall 2023 until spring 2025 she toured with the Joshua Redman Group, including a London Barbican concert in November 2023, and she sings "Era's End" on his next album, Words Fall Short (June 20, 2025). During the same years she appeared on recordings by Al Strong and Sullivan Fortner (Love Stronger, 2022), by Bria Skonberg (a duet on What It Means, 2024) and by the Adonis Rose Trio (For All We Know, 2024).

In August 2024 she signed with Blue Note Records. Her label debut, Diavola, was released on May 1, 2026, co-produced by Redman and Blue Note president Don Was. Redman plays tenor saxophone on two tracks, Jeff Parker plays guitar on nine of the ten songs, Larry Grenadier and Brian Blade are the bassist and drummer on most of the program, and pianist Paul Cornish joins for the last three songs. The ten songs include Bacharach and David's "Raindrops Keep Falling on My Head," "Prisoner of Love," two Italian songs ("Angelo," by Luigi Tenco, and "La notte dell'addio"), a brief Parker instrumental, and two Cavassa originals, "Bossy Nova" and the title track, the latter written with Alexander Warshawsky. She is described in 2026 press as New Orleans-based.

Cavassa is a ballad singer who favors restraint over power: slow tempos, long stretched phrases, careful dynamics and clear diction, with a voice critics describe as intimate and fragile rather than commanding. Don Was likened her singing to a whisper in the listener's ear. AllMusic places her style in jazz, soul and Italian pop, and her stated influences run from Billie Holiday and Phyllis Hyman to Ornella Vanoni and the rock singer Jeff Buckley; she has also named Billy Eckstine as a favorite. Her repertoire crosses jazz standards, pop songs of the 1960s and 1970s, Brazilian and Italian material and her own songs, and Diavola is built around the idea of angel and devil coexisting in one person. Her 2021 Sarah Vaughan competition title and her Blue Note contract mark her as one of the most visible new jazz vocalists of the 2020s.