"I regret what I did," he told the court. "I apologise to the women involved."
Sgarbi, who targeted rich, lonely women, told his lovers he was a special Swiss envoy in crisis zones.
He began an affair with Klatten, who has a personal fortune of around $9.6bn, after meeting her at an exclusive spa near Innsbruck, Austria, in July 2007.
After convincing her to give him money for a girl he said had been left paralysed in a car accident he had caused, he began to demand that the married mother-of-three leave her family and invest $367m in a trust for them to begin a new life together.
When she refused, he threatened to release secret videos of an intimate encounter in a hotel room, and demanded another $62m not to tell her family, later dropping the amount to $17.7m.
But Klatten reported him to the police in January 2008, and he was arrested shortly afterwards.
Sgarbi was also convicted of taking $3m from three other women, whose names were not released, in similar scams.
Thomas Steinkraus-Koch, prosecutor in the case, praised Klatten for coming forward about Sgarbi's attempted blackmail.
"The only victim who came to us and gave a witness statement is Mrs Klatten," he said. "We had to find the others, with great difficulty".
Klatten, the daughter of the late BMW magnate Herbert Quandt, holds a 12.5 per cent stake in the car maker.
She also owns a 88.3 per cent share of chemical company Altana.
Last year, Forbes magazine listed her as the 68th richest person in the world.