The suit filed in Superior Court alleges Costner and Ascendant agreed in December 2004 on pay and movie royalties. The Beverly Hills company then pulled out of the agreement in June, according to the suit.
Calls to Ascendant Pictures late Tuesday were not immediately returned.
The movie was never made. The script was about a grouchy, divorced man who refuses to sell his failing vineyard to the golf course next door.
Costner is seeking $8 million and reimbursement of legal fees.