26-year-old Aaron McKenzie broke into Kelly-Mary Fauvrelle’s family home in June 2019 and stabbed her 21 times in her sleep.
He was also convicted of the manslaughter of her baby son, Riley, who died in hospital four days later, the Old Bailey heard.
McKenzie will be sentenced at the same court on 17 July for the charges of murder, manslaughter, and possession of an offensive weapon.