The football manager beat fellow finalists Emily Atack, who came second, and John Barrowman to take the crown, saying it was “so surreal” to win.
Ten celebrities headed into the Australian jungle in November, where they were later joined by Noel Edmonds.
In the absence of his normal partner Ant McPartlin, Declan Donnelly hosted the show with Holly Willoughby.
More than 11 million votes were cast in the final, Willoughby said.
Redknapp, who follows in the footsteps of previous winners such as Gino D’Acampo and Georgia Toffolo, said: “My grandkids will be jumping around the living room now. They’ll be so excited.”
He said he didn’t think he would survive so long in the show and praised his former camp mates for being “amazing” and pulling him through, adding that he would miss all of his new friends.
Just before he was named the winner, he said: “It’s been an unbelievable experience.”
He said while he has a “very happy home life”, football can be a “lonely business” and that the show had “taught me how to laugh again”.
But he admitted he had struggled with the meagre rations – and unusual foods – and that he thought the contestants would get well-fed with a “nice bit of grub” every night.
She said had been soul-searching and found “so many amazing souls” as well as new-found love and respect for herself.
The Inbetweeners star said: “It’s changed my life in so many ways. I came into this with a bit of a difficult start to the year.
“I didn’t really know what I was doing and where I wanted to go and this place has just given me so me so much self-acceptance.”
Willoughby made the actress promise to never cover up her freckles again, after Atack said: “This is my skin, this is my hair – this is what I look like.”
Barrowman came in third place, and said I’m a Celebrity had been one of the best experiences of his life.
The actor and singer appeared emotional as he told Willoughby and Donnelly: “I can’t tell you how happy I am.”
This year’s contestants have been put through a series of Bushtucker trials involving snakes, cockroaches and other creatures.
They’ve also had to negotiate assault courses blindfolded, bake cakes while plastered in treacle and climb through “sickening sewers” in order to win food and other necessities.
The trio had to each carry out a final trial in order to win treats for their last supper together, after 23 days in the jungle.
Barrowman had to eat a range of gruesome items like worms, a dead spider, goats’ eyes and a bull’s penis.
Atack had to wear a helmet filled with insects while Redknapp’s trial saw him trapped in an underground chamber while rats and bugs ran over him in the pitch black.
Former football manager Redknapp was the bookies’ favourite to win this year’s series, despite having never watched the show before.
After leaving the show and being shown his highlights, he said: “Great show, innit?”
Harry Redknapp wins ITV Series I’m a celebrity.
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