Boonen is expected to rival Mark Cavendish for the green jersey
Belgian rider Tom Boonen has been allowed to enter this year's Tour de France by a French arbitration court.
Organisers had banned Boonen after he tested positive for cocaine for the second time in his career in April.
The 28-year-old's Quick Step team vowed to use "all legal means" to appeal against the suspension.
Boonen is expected to be a main rival to Britain's Mark Cavendish for the best sprinter's green jersey when the race starts on Saturday in Monaco.
Nevertheless, Cavendish welcomed Boonen's inclusion into the three-week race.
"It changes many things, in a good way. Our team will have less pressure in the flat stages," said Cavendish.
Boonen won the Tour de France's green jersey for the points competition the last time he competed in 2007.
But Boonen, who is a celebrity in his native Belgium, was barred from the Tour of Switzerland and Tour de France last year as a result of his first positive test for cocaine in May 2008.
Tour organiser ASO had sought to ban Boonen by saying the Belgian had damaged the race's image after he tested positive for a second time in an out-of-competition test.
He did not face any sanctions from the International Cycling Union (UCI) because it does not hand down penalties for positive out-of-competition tests for the recreational substance.
A second positive test has also left him facing criminal charges and in February this year Boonen was given a suspended sentence by a Belgian court.
But Quick Step have rallied behind their man and have won the argument that cocaine, although illegal, is not considered a performance-enhancing drug.
The arbitration body of the highest sports authority in France, the French Olympic Committee also heard that Boonen's tests were not carried out by the sporting authorities.
"We can confirm the ruling by the French Olympic Committee, and that Tom Boonen will start the Tour de France on Saturday," said a Quick Step spokesman.
"I'm relieved but I'm sorry that we had to go up to here," team manager Patrick Lefevere added.
"The pressure has been huge, not only on Tom Boonen's shoulders, but on the whole team."
Tour de France organisers have yet to react to the news which means there is now no place in the competition for Australian sprinter Allan Davis