Mr Humbard officiated at the funeral of Elvis Presley in 1977
Mr Humbard died of natural causes at a Florida hospital, close to his home.
A former travelling preacher, he began using television to reach his audience in the 1950s and by the 1970s was known across the globe for his services.
Among the admirers of his Cathedral of Tomorrow broadcasts was Elvis Presley and Mr Humbard spoke at the American superstar's funeral in 1977.
"He was the ultimate role model in showing love and caring about other people over and above himself," grandson Rex Humbard III said in tribute.
Vast audience
The son of preachers, Mr Humbard saw the potential of television from early on, making his first broadcast in 1949.
"The vast majority of people do not go to church and the only way we can reach them is through TV," he explained in his book Miracles in My Life. "We must go into their homes - into their hearts - to bring them the gospel of Jesus Christ."
He eventually built his 5,000-seat non-denominational Cathedral of Tomorrow, where he was joined in a programme of preaching and music by his gospel singer wife Maude Aimee.
Regular performers on his shows included Roy Rogers and Dale Evans, Johnny and June Cash.
By the end of the 1970s his programmes were not only broadcast to millions of viewers across the US, but all around the world too.
Hundreds of thousands of people also filled stadiums to hear his message first hand. In 1979 1.2 million people turned out to see him on a tour of Brazil.
Rex Humbard, who for several decades was one of the United States most popular televangelists, died in Florida Friday at the age of 88 of heart failure.

Humbard first conducted television broadcasts of his Christian ministry in 1953. Five years later, the 5400-seat Cathedral of Tomorrow was constructed as the new headquarters for Humbard's weekly church services.