Appearing at The Times Cheltenham Literature Festival, she said: "However you look at it, he is me."
Rendell, made a peer in 1997, said she gave Wexford many of her habits as well as her hatred of corporal punishment and a memory for birthdays.
She also paid tribute to the late actor George Baker who played Wexford on TV series The Ruth Rendell Mysteries.
The 80-year-old, from West Lavington, Wiltshire, died of pneumonia on Friday following a recent stroke.
"Where would Wexford have been without George?" Rendell said.
The actor had "made the popularity and the character - a lot of it was George," she added.
"It was a marvellous achievement as an actor to make him more and better than the author intended," she told the festival.
The Ruth Rendell Mysteries ran for 12 series in the 1980s and 1990s on ITV.
She said that, like her, Wexford liked to walk around in London, read poetry and was tolerant - "but not of cruelty or indifference or callousness".
Rendell's latest novel, The Vault, sees Wexford come out of retirement to try to crack an unsolved crime.
Speaking to the BBC, Baker's daughter, Ellie, said her father "absolutely loved Wexford and he loved being Wexford... and he loved the whole thing. It was a joy to him."
His third wife, Louie Ramsey, who died earlier this year, played his wife Dora in The Ruth Rendell Mysteries.
Author Ruth Rendell has admitted that her famous creation, Ch Insp Reginald Wexford, is based on her.