Lisa, worth a reported $952m, earns an estimated $8.2m a year from the tourism business surrounding Elvis' former home, Graceland. She sold part of the lavish Memphis estate last year for $136m. She met guitarist Lockwood two years ago but she insisted on the pre-nuptial agreement in case the union fails.
A source said: "However much she loves him, she has to protect her fortune."
American celebrity divorce lawyer Raoul Felder told the National Enquirer: "Because of her tremendous wealth, this would be the mother of all pre-nups."
Lisa Marie's new father-in-law told the magazine: "We're really happy."
She was previously married to Nicolas Cage and Michael Jackson. Her first husband and the father of her two children, Danny Keough, was best man at the ceremony in Kyoto on January 22, 2007
One witness said: "You could feel the love. "They were gazing into each other's eyes and stealing little kisses through the service."