She was best known for her novels Georgy Girl and Diary of an Ordinary Woman.
The award-winning author had been suffering from cancer in her back.
Mr Davies, who is also a writer, said: "She had a double mastectomy 40 years ago so she's had a remarkable life considering she had it for so long."
Forster died on Monday morning at the Marie Curie Hospice in north London.
Confirming her death, the couple's daughter Caitlin Davies wrote on Twitter: "Our lovely mum Margaret Forster died this morning. Her books will live on."
Margaret Forster was born in Carlisle, and was a teacher at a girls' school in Islington before her writing career took off.
Her most famous novel Georgy Girl, published in 1965, was turned into a film starring Lynn Redgrave and Charlotte Rampling the following year.
The book told the story of a young woman in 1960s London who is pursued by two different men - her father's employer and the young lover of her pregnant flatmate.
'Remarkable woman'
Fellow novelist Elizabeth Day paid tribute to Forster, saying she was "an under-appreciated wonder of a writer who was once very nice to me as a debut novelist".
Forster's most recent book was My Life In Houses, published in 2014 - an autobiographical tour of places she had lived including Oxford, Portugal, the Lake District and what she described as the "wrong side" of Hampstead in London.
Across her career, the author published more than 25 novels, plus several biographies of figures including Dame Daphne du Maurier and 19th Century novelist William Makepeace Thackeray.
Speaking to the Press Association, Davies described his wife as "the cleverest woman I ever met".
"She was emotionally clever, in that she could always understand people and predict their actions and their feelings and their motives, which I can never do. And she was a brilliant critic as well.
"Always had an opinion whether asked for it or not, and she was just the most marvellous woman. She was a remarkable woman in every way."
Mr Davies said his wife rarely gave interviews as she "was not interested in publicity".
But Forster did appear on Radio 4's Desert Island Discs in 1994.
The writer Margaret Forster has died at the age of 77, her husband Hunter Davies has announced.