Her many fans have always had difficulty with the known portraits of Jane Austen.
Dr Byrne, who is currently writing a biography of the 18th novelist, said that the best known picture, known as the "memoir portrait" had "always rather annoyed" her.
"It makes her look pretty and dim," she told the Christmas Radio Times.
"It feeds this whole notion of 'Aunt Jane', the demure spinster who was very good at spillikins and enjoyed scribbling on the side, but was content with her life in the shadows.
"Scholars know there was so much more to her. And for me this new picture encapsulates – almost too perfectly – that other side.
"She's a professional woman presenting herself to the world with the tools of her trade. It's the image of Jane Austen so many of us have been waiting for."
Dr Byrne was midway through her new book when her husband – the renowned Shakespeare scholar Prof Jonathan Bate – surprised her with a portrait of a female writer bought at auction.
She spotted the long, straight "Austen nose" seen in images of the writer's father and brothers and enlisted the help of a team of experts and the BBC to test her as yet unproven thesis that the woman is the famous author.
Her find is the subject of a new BBC TWO documentary, Jane Austen: The Unseen Portrait?, to be broadcast on Boxing Day.
The only known images with proven provenance of the author of Sense And Sensibility, Pride And Prejudice and Emma to date are Austen's sister Cassandra's 1810 sketch, in which the writer is said to look a little cross, and an "idealised" portrait used as the frontispiece to the Austen memoir written by her nephew in 1870.
Dr Byrne, whose Austen biography, The Real Jane Austen, is being published in 2013, believes the new portrait could transform the author's image.
Dr Byrne, whose previous work includes Jane Austen And The Theatre, and Perdita: The Life of Mary Robinson, said she had a jolt of recognition as soon as she saw the image.
"My immediate reaction was, 'My God, it's Jane Austen!'. "It was the nose that did it," she said.
"I am absolutely so confident this is her."
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