Prosecutor Iain Simkin KC told jurors: "Tiffany Render had become conditioned to obedience, was in thrall to the defendant and, irrespective of the risks to her own well-being, nevertheless visited him on March 22."
Irwin had twice been arrested and bailed by police with conditions not to contact Miss Render in the weeks before her murder.
He called the ambulance service, claiming he had woken to find Miss Render dead.
In evidence, Irwin, of George Street, described suffering from paranoid schizophrenia, which caused him to hear voices and hallucinate. But he insisted his condition was fully medicated and under control in March.
Irwin claimed Miss Render's death was accidental, but during the trial he pleaded guilty to manslaughter and also admitted sexual assault.
Judge Mrs Justice Foster heard a psychiatric report had been provided to the court by Irwin's legal team but announced she would not pass sentence immediately.
She described it as a "distressing" case and told jurors they would be discharged from serving on future crown court trials for life.
Irwin will be sentenced in the week of 16 December and was remanded in custody.