It overturned the decision of the Amaury Sport Organisation (ASO), the Tour organiser, to exclude the Quick Step sprinter because of his positive out-of-competition tests for cocaine. The court's decision cannot be appealed.
Quick Step team manager, Patrick Lefevere, was not in Paris when the Court's ruling was handed down, but he was understandably happy to hear the news that his highest profile rider would be allowed to start cycling's biggest event.
"I did not believe it was justice [to exclude Boonen]," Lefevere told Cyclingnews on Friday. "But the correct decision has now been made."
Boonen is already in Monaco, having travelled there with the Quick Step team in anticipation of the CAS decision.
Lefevere confirmed that Australian, Allan Davis, who was on stand-by to take Boonen's place at the Tour in the event of the CAS ruling against Boonen, had returned to his home in Spain on Friday afternoon.
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