Rocky Taylor, a friend of 40 years standing, said the former BBC radio DJ and Crackerjack presenter had died in hospital in Bournemouth.
Stewart's former brother-in-law, Adriano Henney, tweeted to say "Fun guy-Huge loss".
Director of BBC Music Bob Shennan said Stewart had been a "stalwart" of popular music broadcasting.
Mr Shennan said Stewart's shows had been enjoyed by millions of listeners.
Ed 'Stewpot' Stewart: Your memories
Stewart's BBC Radio 2 colleagues were extremely saddened, he said, adding: "We are thinking of Ed's friends and family at this difficult time."
Stewart's fellow DJ from his early days on pirate radio, Tony Blackburn, who also went on to Radio 1, said Stewart would be missed.
"A lovely guy, loved his golf and he loved playing the songs on Junior Choice.
"I think he'll probably be best remembered for Junior Choice because he did that programme, I think, particularly well.
"He was very, very good at that, and of course, on television."
His former colleague and friend of 50 years, BBC DJ David Hamilton, said Stewart "was a little bit like a good wine; he just got better as time went on".
The DJ, also known by the nickname "Diddy", said he spoke to his old friend just a few days ago.
He said: "We used to play football together in the showbiz football team, we even once rode in a speedway race together at Wembley Stadium, so we've done a lot of things together.
"He was a really good guy, Ed, and I really will miss him."
His younger sister, Sue Mainwaring, 69, described him as hardworking, loyal and "such a good brother".
"We had such fun. When he was on the pirates [radio stations] he had two weeks on and one week off - of which every weekend he'd invite everybody back for jazz sessions. Celebs used to come along, including Kenny Everett, David Hamilton, Tony Brandon. He loved jazz. He loved music."
She said she had spent Christmas and New Year with him and other members of the family.
Devon-born Stewart's broadcasting career spanned more than 50 years. He started out as an announcer, film critic and rugby reporter with Radio Hong Kong.
In an interview with the Express newspaper in 2014, he said he had returned to England five years later and joined pirate radio ship Radio London, based four miles off shore.
He was one of the first presenters on Radio 1 when it launched in 1967, and went on to become a regular Top of the Pops presenter in the 1970s.
He was a regular Radio 2 presenter for 15 years, and during that time broadcast from the summits of Ben Nevis and Snowdon, Mount Vesuvius volcano in Italy, and also live from the Falkland Islands.
On television, Stewart was best known for children's favourite Crackerjack. He hosted the show from 1973 to 1979.
He was also a longstanding presenter of children's show Junior Choice, which last broadcast on BBC Radio 2 over Christmas.
On it he coined his trademark catchphrase: '''Ello darling."
In his sign-off at the end of his final programme, he thanked listeners, saying: "I'll be with you whenever, but have a great Christmas Day, won't you, folks?"
Off air, he was a keen golfer and dedicated Everton FC fan.
On Twitter, TV presenter Noel Edmonds left heartfelt messages about the man he called his "mentor".
Edmonds joined BBC Radio 1 in 1969, taking over from the sacked Kenny Everett in 1970. At 21, he was the station's youngest DJ at the time.
"In '67 Ed Stewart heard a DJ audition tape, liked it, passed it to Kenny Everett and my career was born. Stewpot I owe you everything xN," he tweeted.
Former Radio 1 DJ and current Radio 2 broadcaster Simon Mayo wrote in a tweet: "How sad to hear of the passing of Ed Stewart.  Junior Choice was always a radio classic".
Celebrity astrologer Russell Grant tweeted: "So sad to hear an old DJ colleague of mine Ed Stewart 'Stewpot' has passed over.
"I last worked with him on Radio Mercury. Happy memories."
Coronation Street actor Les Dennis posted: "Sad to hear Ed "Stewpot" Stewart has died. A great broadcaster and a nice man."
Stewart is survived by his two children, Francesca and Marco, and four grandchildren.
Former BBC DJ Ed "Stewpot" Stewart has died at the age of 74, a few days after having a stroke, friends have said.