"By using Ryanair's database" lastminute.com and Lmnext FR, the British company's French operation, "have committed an act of parasitism," the court said in a judgement dated March 20, of which AFP obtained a copy.
Ryanair in a statement welcomed the ruling for putting a halt to the "free ride" of its website without consent.
Ryanair spokesman Robin Kiely said the airline urges consumers "to avoid 'screenscrapers' such as lastminute and book directly on the Ryanair website,
the only place to find the cheapest Ryanair fares."
The case was brought after Ryanair introduced restrictions on the use of its website.
These restrictions include banning travel agencies from buying Ryanair flight tickets from its online site.
The Paris court ordered the two lastminute companies to pay Ryanair 50,000 euros for the offence, with a further 1,000 euros ($1,200) per day payable if the "parasitism" doesn't stop.
On top of that the online travel agent was ordered to pay 10,000 euros towards Ryanair's costs in the case.
"We welcome this Paris Commercial Court ruling upholding Ryanair's right to determine its own distribution model which is guaranteed under the constitutional freedom of trade and industry in France," Ryanair said in its statement.
The lastminute company, which has a month to appeal the decision, could not immediately be contacted for comment.