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.

Grégory Villemin was four when his body was found in the Vologne river. His killer has never been found.
All three held by police were described as relatives of the boy's father.
The murder has continued to haunt France ever since, but advances in DNA technology have helped police shed further light on the case.
It was on 16 October 1984 that Grégory Villemin's body was found and a magistrate opened what became one of the biggest mysteries in French criminal history.
Hours before the boy was discovered, his hands and feet tied, his uncle said he had received a phone call from someone claiming to have kidnapped him. The following day, the child's parents received a letter that said: "Your son is dead, I have been avenged."
The next month, a cousin of the boy's father, Bernard Laroche, was arrested when his sister-in-law, Muriel Bolle, testified against him. He was released in 1985 when she retracted her statement, but shot dead by Jean-Marie Villemin, the boy's father, weeks later.
The father went to jail for Laroche's murder for several years. The boy's mother, Christine Villemin, was also jailed for her son's murder but later cleared. Both were later given compensation by the state for miscarriage of justice.
The anonymous phone-calls and poison-pen letters continued over the years, and the case was reopened first in 2000 and then again in 2008 in an attempt to identify the DNA on the letters. Three separate traces of DNA were found but not identified.
Little news has been heard in the "Grégory affair" since police said in 2013 that DNA tests had brought the investigation no further.
That was until about 08:00 (06:00 GMT) on Wednesday, when investigators from Dijon detained a couple in their 70s in the village of Aumontzey, in the Vologne river valley. Sources told French media that they were the father's uncle and aunt.
They were placed in police custody on suspicion of complicity in the murder, failing to report a crime or helping a person at risk, according to L'Est Républicain website.
A third person reported to be the father's half-sister was also being held. A fourth, said to be the victim's grandmother, was taken in as a witness. Her husband was also questioned.
Prosecutor Jean-Jacques Bosc said investigators had targeted "people very close to the heart of this case" and hoped to provide answers to the questions they had.
Local reporters covering the case pointed out that none of those held on Wednesday was suspected of the boy's murder.
They also said that Muriel Bolle, who as a teenager had initially blamed the killing on Bernard Laroche, had been asked to provide a DNA sample on Wednesday before later being released.
Author Ruth Rendell has admitted that her famous creation, Ch Insp Reginald Wexford, is based on her.
[NEXT_CONCEPT]
A couple in their 70s and a woman have been detained for questioning by police, 32 years after a crime that horrified France.