Leny de Andrade Lima was born January 25, 1943, in Rio de Janeiro. Her mother was a music teacher, and Andrade began classical piano lessons as a child, later winning a scholarship to the Conservatório Brasileiro de Música. She was singing publicly by age nine, appearing on the Rádio Tupi program Clube do Guri with Ary Barroso's "Risque." Her half-brother Dudu, a saxophonist and flautist, brought her into contact with working musicians and the clubs where they played, and as a teenager she became fascinated with the wordless vocal improvisation of singer Dolores Duran, an early model for the scat technique she would carry through her entire career. In 1958, at fifteen, she began singing professionally as a crooner with Permínio Gonçalves's orchestra.

By 1961 Andrade was a fixture of the nightclubs along Beco das Garrafas in Copacabana, performing at the Bacará with an early trio led by Sérgio Mendes and singing at the nearby Bottles Bar. Her debut album, A Sensação, was released that year by RCA Victor, and she was already using scat on the record. She joined pianist and bandleader Dick Farney's orchestra in São Paulo in 1962, and her second LP, A Arte Maior de Leny Andrade (1963), featured drummer Milton Banana. She had already sung outside Brazil by then, including a short engagement in Buenos Aires. In 1965 she joined singer Pery Ribeiro and the group Bossa Três for Gemini V, a nightclub revue at Rio's Porão 73 directed by Ronaldo Bôscoli and Luiz Carlos Miele, released as a live album; she also recorded Estamos Aí the same year.

Gemini V toured to Mexico City, and Andrade relocated to Mexico in 1966, working frequently with Ribeiro before returning to Brazil in the early 1970s. She picked up bolero as a permanent part of her repertoire while in Mexico, and it was there that she met Ella Fitzgerald and Sarah Vaughan, two singers she would be compared to for the rest of her career. Back in Brazil, she reunited with Ribeiro for Gemini Cinco Anos Depois (1972), which included Antônio Carlos Jobim's "Águas de Março," and her catalog through the decade leaned further into samba and MPB: Alvoroço (1973) and Registro (1979), the latter including Johnny Alf's "Nós."

In 1983 Andrade recorded the double live album Leny Andrade ao Vivo, cut at the RCA Victor auditorium in Rio and featuring "Cantor da Noite," written for her by Ivan Lins and Vitor Martins. That same year she made her New York debut at the Blue Note, backed by drummer Portinho, trumpeter Claudio Roditi, pianist Aluizio Milanês and bassist Lincoln Goines; a New York Times review praised the speed of her scat singing and compared it directly to Fitzgerald's. She followed with a run of Brazilian and American-songbook records through the decade's end, including a tribute to composer Cartola, Luz Neon, 1991's Bossa Nova, and Embraceable You, recorded in the Netherlands for the Dutch jazz label Timeless, setting American standards in Brazilian arrangements. In 1992 she spent four nights at the Ballroom in Manhattan to strong reviews, and she kept an apartment in New York for years afterward, returning often to American stages including Birdland, Jazz at Lincoln Center and the Hollywood Bowl.

The 1990s brought a run of recurring musical partnerships: Nós with pianist César Camargo Mariano, Maiden Voyage with pianist Fred Hersch (Chesky Records, 1994), and the voice-and-guitar record Coisa Fina with guitarist Romero Lubambo, followed by a 1995 album of Jobim songs with pianist Cristóvão Bastos and Luz Negra, a collection of Nelson Cavaquinho compositions. She returned to Lubambo for Lua do Arpoador in 2006 and reunited with Camargo Mariano for Ao Vivo, recorded at the Teatro Guaíra in Curitiba, which won the 2007 Latin Grammy Award for Best MPB Album. In 2009 she and Lubambo performed at the Umbria Jazz Festival in Italy. In 2014 she recorded Alegria De Viver, a duo album with the Israeli-American jazz guitarist Roni Ben-Hur for Motéma Music, drawing on the bossa nova songbook rather than the most familiar standards; she returned as a guest vocalist on Ben-Hur's Samba Do Arraial in 2020.

Falls made performing more difficult as she aged; in May 2016 she stumbled walking onto the stage at Birdland but finished the show, and she increasingly performed seated in the years that followed. She moved into the Retiro dos Artistas, a home for retired performers in Rio, in 2019 by her own choice, and continued to rehearse and perform there. In August 2022 she returned to the studio with pianist Gilson Peranzzetta to record "Por Causa de Você," a song by Jobim and her early influence Dolores Duran that she had sung for years but never recorded; the single was released in January 2023, around her 80th birthday. Andrade had been living with Lewy body dementia and was treated for pneumonia in June 2023. Her health worsened afterward, and she was admitted to the Hospital de Clínicas de Jacarepaguá in Rio, where she passed away on July 24, 2023, at age 80.

Andrade sang with a low, husky voice and a forcefulness that set her apart from bossa nova's typical hushed delivery; composer Carlos Lyra said her singing carried the swing of Sarah Vaughan, Ella Fitzgerald and Carmen McRae rather than the genre's lighter vocal style. Scat was central to her music from the start, modeled initially on Dolores Duran's wordless improvising. A 2013 master's thesis by musicologist Lívia Scarinci Nestrovski, analyzing her 1958-1965 recordings, found that Andrade retained jazz scat's improvisational structure while shaping it with syllables and accents closer to Brazilian Portuguese and samba, a hybrid the thesis termed "Brazilian scat singing" and that AllMusic's own catalog copy shorthands as "samba-jazz." Her American engagements were reviewed on those same terms for decades: the 1983 Blue Note debut drew a direct comparison to Fitzgerald in the New York Times, her 1992 Ballroom run drew comparisons to Vaughan, and after a 2008 set at Birdland, critic Stephen Holden wrote in the Times that her voice "seems to contain the body and soul of Brazil." Tony Bennett called her "one of the greatest improvisers in the world." Her standing among jazz musicians is also marked by a direct tribute: saxophonist Paquito D'Rivera wrote and recorded the composition "For Leny (Andrade)" on his 1987 album Manhattan Burn.