Ms Smith, who was previously married to country music singer and TV executive Chester Smith, described the engagement as a “gift from God”.
She said: “I’m a widow 14 years. Like Rupert, my husband was a businessman. Worked for local papers, developed radio and TV stations and helped promote Univision.
“So I speak Rupert’s language. We share the same beliefs.”
Mr Murdoch proposed in New York on St Patrick’s Day, joking that he is “one-fourth Irish”. The billionaire told the New York Post he personally selected an Asscher cut diamond for the engagement ring.
The wedding is scheduled to take place this summer. The couple will divide their time between the UK, California, New York and Montana.
Mr Murdoch’s six-year marriage to former supermodel Jerry Hall ended last year. Ms Hall was reportedly handed the keys to an £11m Oxfordshire mansion and a home in the south of France, as well as a cash sum, as part of the divorce settlement.