Ramsay accused his father-in-law, Christopher Hutcheson, of using an autopen machine to forge his signature on a document making Ramsay personal guarantor for the rent on the York & Albany pub, now a fashionable dining spot.
But High Court judge Paul Morgan ruled that the contract was binding. He said that when the 25-year lease was signed in 2007, Hutcheson "was acting within the wide general authority conferred on him by Mr. Ramsay" to manage his business.
He said Ramsay knew that the autopen — a device often used by authors to sign multiple copies of their books — was "routinely used to place his signature on legal documents."
"I hold that Mr. Ramsay, acting though his agent Mr. Hutcheson, is bound by the guarantee in the lease of the premises," the judge said.
Ramsay fired Hutcheson, the father of his wife Tana, in late 2010, accusing him of gross misconduct.
The judge ordered Ramsay to make an interim payment to the pub's owner, Gary Love, of 250,000 pounds. The chef also faces a large bill for legal costs.
Morgan denied Ramsay permission to appeal, but the chef can ask the Court of Appeal directly to hear the case.
Ramsay is internationally known for a string of acclaimed restaurants, popular cookbooks and television shows including "Kitchen Nightmares," ''Hell's Kitchen" and "The F Word."