Walter José Wanderley Mendonça was born in Recife, Pernambuco, on May 12, 1932. He began working as a professional musician in his home state and moved to São Paulo at the end of the 1950s, where he played organ in nightclub bands, among them the house group at the Bar Claridge and later the band at the Boate Oásis, where the singer Isaurinha Garcia brought him in. She became his wife, and by the 1940s and 1950s she was one of the best-known singers in Brazil. His first recorded appearance, in 1959, was as organist on a track of one of her Odeon records.

In 1960 he took a job at the Captains Bar of the Hotel Comodoro with a group billed as Walter Wanderley e seu Conjunto, and the band accompanied singers on records and television programs, among them Garcia, Dóris Monteiro and João Gilberto. Wanderley's group is the one heard on part of Gilberto's 1961 Odeon album João Gilberto. His own LPs for Odeon followed in quick succession: Eu, Você e Walter Wanderley (1960), Sucessos Dançantes em Ritmo de Romance (1961), O Sucesso é Samba (1961), Samba é Samba and E o Bolero (1962), and O Samba é Mais Samba and Samba no Esquema (1963). In 1964 he changed the makeup of his group and signed with Philips, which issued Entre Nós, Órgão, Sax e Sexy (made with the saxophonist Portinho) and O Toque Inconfundível de Walter Wanderley that year, then O Autêntico Walter Wanderley, Samba Só and Quarteto Bossamba in 1965.

The record that made his name outside Brazil came in 1966. By the account on English Wikipedia, the producer Creed Taylor brought Wanderley's trio to the United States at the urging of Tony Bennett. The trio was Wanderley on organ, Claudio Slon on drums and José Marino on bass, and it recorded for Verve under Taylor's production. The first album, Rain Forest (Verve V6-8658), included an instrumental treatment of "Summer Samba," known on the record label as "So Nice." Marcos Valle had written the song in 1964 with Portuguese words by his brother Paulo Sérgio Valle, and Wanderley's organ version first charted in August 1966, reaching No. 3 on Billboard's Easy Listening chart and No. 26 on the Hot 100. Rain Forest reached No. 22 on the Top LPs chart. Alongside the trio, the album used a small group of American jazz and studio players: Joe Grimm on flute, Bucky Pizzarelli on guitar, Urbie Green on trombone and Bobby Rosengarden on percussion, with Rudy Van Gelder engineering. Bennett's endorsement appeared on the back cover, where he told listeners who liked Ella, Duke, Basie and Sinatra that they would love Wanderley's music.

Taylor paired the trio with Astrud Gilberto for A Certain Smile, a Certain Sadness, recorded in September 1966 and issued by Verve at the height of the American bossa nova craze. Wanderley recorded six albums for Verve between 1966 and 1968. After Rain Forest and the Gilberto collaboration came Chegança (1967) with the same trio, then Batucada and Kee-Ka-Roo in 1967, and Popcorn (1967), a collaboration with the Brazilian singer and guitarist Luiz Henrique Rosa. In the same period he formed a band called The Carnival with Bob Matthews, João Palma, José Soares and Janis Hansen, all former members of Sérgio Mendes's Brasil '66.

When the trio ended, Wanderley kept recording. When It Was Done (1968, credited to the Walter Wanderley Set) and Moondreams (1969) came out on A&M with the CTI imprint, and the trio reunited briefly in 1971 for The Return of the Original. His later records were made for GNP Crescendo, including Brazil's Greatest Hits! (1980) and Perpetual Motion Love (1981). He also made numerous personal appearances, including a concert tour of Mexico. English Wikipedia says that alcoholism blighted his later career. He passed away from bone cancer on September 4, 1986, in San Francisco, aged 54.

Wanderley belongs to the crossover side of Brazilian music, and the pop side of it is plain: the records that reached an American audience were short, melodic organ instrumentals of familiar bossa nova and samba songs, built for radio and for the lounge. What distinguishes them is the playing. He worked mainly on the Hammond B-3, and on later records and in concert on a Hammond L Series, with a staccato, stuttering articulation that sounds nothing like the sustained, blues-based organ of the American soul-jazz players. The jazz side of the work is in the company he kept on the sessions: a trio with a swinging bass and drums rhythm section, Creed Taylor's production at Verve and CTI, and sidemen such as Urbie Green and Bucky Pizzarelli. The Verve sessions also drew on the repertoire of the Brazilian songwriters of his own generation and the one before it, including Marcos Valle, Antonio Carlos Jobim, Durval Ferreira and Oscar Castro-Neves. Tony Bennett's cover blurb is the clearest period statement of how he was heard, and a later AllMusic reviewer, Thom Jurek, wrote that his "Summer Samba" is regarded as perhaps a more definitive bossa nova tune than "The Girl from Ipanema."