The decorated Chicago icon was an accountant before striking gold with comedy, acclaimed for his dry, deadpan delivery.
He died at his Los Angeles home after a series of short illnesses, his longtime publicist Jerry Digney said in a statement.
Born September 5, 1929, in suburban Illinois, Newhart studied business management before being drafted into the US army and serving in the Korean War.
He briefly studied law before quitting and getting work as an accountant, while moonlighting as a comedy performer and writer.
"In 1959, I gave myself a year to make it in comedy; it was back to accounting if comedy didn't work out," he has said.
It did -- he was signed to Warner Bros. Records, and "The Button-Down Mind of Bob Newhart" became the music industry's first comedy album to hit the top of the sales charts.
It earned him prestigious Grammys for Best New Artist and Best Album, and helped launch his career in television. The recording is now archived in the Library of Congress.
'The Sound of Laughter'
Newhart starred in two long-running sitcoms in the 1970s and 1980s, and made guest star appearances into his 90s.
He featured as a recurring guest on "The Big Bang Theory" and also starred as Papa Elf in the Christmas film "Elf."
The second of his sitcoms -- the eight-season "Newhart" -- closed in one of the most memorable series finales of all time.
In the final episode, Newhart's character wakes up in bed with his wife from the first sitcom, telling her about a strange dream -- the plot of the second show.
The stunt parodied a famous plot element from the series "Dallas."
Newhart is survived by four children. His wife of six decades, Virginia, died in 2023.
"Comedy has given me a wonderful life. When I first started out in stand-up, I just remember the sound of laughter," he once said.
"It's one of the great sounds of the world."
