Mr. Gilberto performs at Carnegie Hall in Manhattan in 2004. (Mary Altaffer/AP)

João Gilberto, a Brazilian guitarist and singer who helped define the subtle, swaying and quietly sensuous style of music known as bossa nova, which became a worldwide craze in the 1960s, died July 6 at his home in Rio de Janeiro. He was 88.

His son, João Marcelo Gilberto, announced the death on social media but did not provide a cause. His father had been in declining health for several years.

Mr. Gilberto began his musical career in the 1940s, but it wasn’t until the mid-1950s that he developed the distinctive understated vocals and syncopated rhythms that would become known as bossa nova. (Loosely translated, the term means “new wave” or “new trend.”)

Once he joined forces with composer and performer Antonio Carlos Jobim, that wave began to crest. His 1958 recording of Jobim’s “Chega de Saudade,” sung in an intimate style without vibrato, became Mr. Gilberto’s signature tune and launched the bossa nova movement. Singing in Portuguese, he conveyed a mood of both longing and regret in the lyrics by Vinicius de Moraes, roughly translated, in part, as:

But if she comes back, if she comes back

What a beautiful thing, what a crazy thing

For there are less fish swimming in the sea

Than the kisses I’ll give you

“All I can say is that it was like the first time I heard Charlie Parker,” Brazilian guitarist Oscar Castro-Neves told the Los Angeles Times in 2003. “It changed everything, for every young musician in Brazil. Once we heard what João was doing with the guitar and the voice, we all had to find a way to figure out how he did it.”

Derived from Brazil’s traditional samba music and the melodic cool jazz of the 1950s, bossa nova gained further exposure in the 1959 film “Black Orpheus,” with a soundtrack by Jobim and Luiz Bonfa. American jazz musicians soon adopted the new style, and in 1962 guitarist Charlie Byrd and saxophonist Stan Getz recorded “Jazz Samba” at Washington’s All Souls Unitarian Church. The album spent more than a year on the pop charts, reaching No. 1.

In 1963, Mr. Gilberto and Getz recorded an album, “Getz/Gilberto,” that was not released until a year later. The first voice heard on the album’s most famous song, Jobim’s “The Girl From Ipanema,” is that of Mr. Gilberto, singing de Moraes’s Portuguese lyrics while gently strumming his guitar.

He sets a tone of breezy, sun-dappled nonchalance that is picked up in an English-language verse sung by Mr. Gilberto’s wife at the time, Astrud Gilberto, and later by Getz’s soaring tenor saxophone. The song became an international hit. The “Getz/Gilberto” album sold more than 1 million copies and received several Grammys, including Album of the Year.

“João probably single-handedly did more for Antonio Carlos Jobim than any other artist could have done,” record producer Tommy LiPuma, who made an album with Mr. Gilberto in the 1970s, told the Los Angeles Times. “Nobody knew what to do with those songs like he knew what to do with them. I’ve never heard anybody do them as well or interpret them in the manner he has.”

A follow-up album, “Getz/Gilberto II,” was released in 1966, but Mr. Gilberto was never comfortable with the fame that came his way. He remained aloof, comfortable only when delving deep into his music in a private, almost reverential way. He sometimes stopped his performances if audience members were speaking or canceled engagements if a club or concert hall was too noisy.

“When I sing, I think of a clear, open space and I’m going to play sound in it,” Mr. Gilberto told the New York Times in 1968, in a rare interview. “It is as if I’m writing on a blank piece of paper. It has to be very quiet for me to produce the sounds I’m thinking of. If there are other sounds around, the notes I want won’t have the same vibrations.”

Mr. Gilberto “carries reserve to an unusual extreme for a performer,” Times critic John S. Wilson wrote in 1968, but he “has gauged his art so skillfully that the listener is caught up in the mood and the effect becomes almost hypnotic.”

He performed Jobim’s music, his own songs, works by older Brazilian composers — and the occasional unexpected show tune such as “The Trolley Song,” which he muted in his own hushed style.

Mr. Gilberto released four more albums in the 1970s and had a reunion with Getz in 1976. In the liner notes to “Getz/Gilberto ’76,” a live recording released in 2016, author James Gavin described Mr. Gilberto’s relaxed yet powerful musical presence: “His vibratoless, nasal-toned, sotto voce croon floated with seeming detachment above his guitar. The push-and-pull between the two was a marvel of rhythmic and melodic tension and release. . . . His music was wistful but cool; Gilberto was a man of secrets.”

João Gilberto do Prado Pereira de Oliveira was born June 10, 1931, in Juazeiro in the northeastern Brazilian state of Bahia. His father was a prosperous businessman.

Mr. Gilberto had few interests beyond music and was captivated from an early age by what he heard on the radio — from the American music of Duke Ellington, Tommy Dorsey and Frank Sinatra to traditional Brazilian music.

He began singing in groups in Bahia’s capital of Salvador and later in Rio de Janeiro, but he was often late or absent and was ultimately fired. For several years, he stayed with friends and relatives, not holding a job and smoking huge amounts of marijuana.

After his family briefly sent him to a psychiatric hospital, he stopped using drugs and eventually began performing at a club in the city of Porto Alegre. He practiced long hours in his sister’s bathroom, learning to sing softly without vibrato while developing a complex, fingerpicking style of guitar playing.

By 1956, he had returned to Rio de Janeiro, where he teamed up with Jobim. Several other composers and performers took part in the development of bossa nova, but it didn’t receive its fullest expression until Mr. Gilberto’s version of “Chega de Saudade.”

His marriage to Astrud Gilberto (nee Weinert) ended in divorce. In 1965, he married Heloísa Maria Buarque de Hollanda, a singer known as Miúcha. They later separated.

Survivors include a son from his first marriage; a daughter, singer Bebel Gilberto, from his second marriage; and a daughter from another relationship.

In 1997, Mr. Gilberto sued the EMI record label because he thought a reissue of some of his early music had been botched. In later years, he had financial problems, but his place in Brazilian culture was secure.

Mr. Gilberto lived in the United States and Mexico before returning to Brazil in the early 1980s. He performed in the United States in the 1990s and early 2000s before giving his final performance in 2008.

“I owe João Gilberto everything I am today,” Brazilian pop singer Caetano Veloso told the Los Angeles Times in 2003. “Even if I were something else and not a musician, I would say that I owe him everything.”