The Corriere della Sera newspaper said the €36 million-a-year settlement was filed with a court in Milan.
No comment was immediately available from the court or from lawyers for either Mr Berlusconi or Ms Lario.
Ms Lario, a former actress who was married to Mr Berlusconi for more than 22 years, asked for a divorce from the 76 year-old in 2009, accusing him of having an affair with a 17 year-old girl.
She had already delivered a public rebuke to her billionaire husband over his relations with other women, sending an open letter to the daily La Repubblica in 2007 in which she said he owed her a public apology after injuring her dignity as a woman.
Mr Berlusconi has been accompanied by repeated allegations of sexual scandal, culminating in accounts last year of "bunga bunga" sex parties in his Milan home and charges of paying for sex with a juvenile prostitute, which he denies.
Ms Lario had originally asked for a monthly alimony of €3.5m, while Mr Berlusconi had offered no more than €300,000 a month.
The Corriere della Sera said the settlement would not give Ms Lario a villa worth €78m near Brianza in northern Italy, where she raised their three children.