His Facebook page said Jarreau "passed away this morning, at about 600am LA time. He was in the hospital, kept comfortable by his wife, son, and a few of his family and friends."
No cause of death was given.
Jarreau was hospitalized for exhaustion last week and forced to cancel his remaining tour dates for 2017. He announced on Wednesday he was giving up touring.
A post on his Facebook page on Thursday said he had been "recovering slowly and steadily."
"His son reports that he caught his dad singing 'Moonlighting' to one of the nurses the morning ... a very encouraging sign," the post said of the theme song to the 1980s American television show starring Bruce Willis and Cybill Shepherd.
The "Moonlighting" theme, for which he wrote the lyrics, cemented his place in pop culture.
Jarreau was considered one of jazz's greatest vocalists, with a mastery of scat singing and vocal percussion. But his smooth, breezy hit "We're in This Love Together" from the 1981 album "Breakin' Away" made him a mainstream commercial success.
Jarreau died hours before Sunday's Grammy Awards, the biggest night of the year for the music industry.
"Breakin' Away" won the Grammy for Best Pop Performance. He also won Grammys for best jazz vocal performance, best pop vocal performance, best R&B vocal performance, and most recently in 2006 for best traditional R&B vocal performance along with George Benson and Jill Scott for "God Bless the Child."
"Rest in power, @AlJarreau," fellow singer Chaka Khan wrote on Twitter. "U were EVERYTHING Jazz & beyond with an unrivaled improvisational genius. Love & prayers 2 his family & fans."
Born Alwin Lopez Jarreau in Milwaukee on March 12, 1940, his first album came out in 1975 and he made his Billboard chart debut in 1981 with "We're in This Love Together," Billboard.com reported.
The song was his highest-charting hit, reaching No. 15 in November 1981, Billboard said.
He was also one of the stars to sing on the single "We Are the World" to raise money for famine relief in Africa, getting a solo line between Willie Nelson and Bruce Springsteen.