The 52-year-old broadcast journalist said she was "amazed, astonished and gobsmacked" at her victory.
Thatcher was one of 10 celebrities, including former soap opera stars and pop singers, to endure a series of humiliations in the Australian rain forest.
"I'll treasure happy memories of cooperation, kindness, good humor, banter and so on," she said Monday night. "I shall definitely remember eating a squelching kangaroo testicle."
The public voted contestants off the show based on their performance in endurance tests usually involving bugs and wildlife. Thatcher ate fish eyes and swam across a lake with poisonous frogs, snakes and rats on her head — twice — to win dessert for her fellow campers.
She started the show by throwing up on herself while skydiving into the jungle and made headlines when she was caught on camera urinating next to her camp bed.
But her co-stars had nothing but praise for her, including singer Jimmy Osmond, who said she was "bigger than life."
Thatcher said her mother, known as the "Iron Lady" when she was prime minister from 1979 to 1990, didn't know she was on the show.
"I left my mother's home phone number behind, so I don't even know her number," she said. "She doesn't know I'm here so she won't notice."