Murphy failed a drugs test at Chantilly on July 19, but has always strenuously denied taking any banned substance.
Following a hearing on Wednesday, France Galop has imposed the suspension, which runs from December 11 until March 11.
A statement from the authority said: “France Galop stewards have banned Oisin Murphy from race-riding for three months after a biological sample taken on July 19, 2020 at Chantilly revealed the presence of cocaine metabolites.
“In accordance with the rules of racing of France Galop, the ban will take effect from December 11, 2020 until March 11, 2021 inclusive.
“This decision takes into account the defence and scientific evidence presented by the jockey and his counsel during a hearing on November 25, 2020 at the France Galop headquarters.”
No appeal
Murphy has announced he will not appeal against the suspension, which ends before the Flat Turf season begins in Britain on March 27.
In a statement issued through the Professional Jockeys Association, he said: “I would like to thank France Galop and the panel of Commissioners for a fair hearing and for accepting the evidence I presented that I had not taken cocaine.
“This evidence included my hair sample results – the results of which I am making public today – and an expert witness statement from an eminent toxicology and anti-doping expert.
“Whilst I am obviously disappointed that I will still have to serve a three-month suspension, I am pleased the Commissioners accepted the evidence presented and am hugely relieved to have been cleared of taking cocaine.
“I respect the rules of France Galop, respect their decision and will not be appealing. Despite my relief, I regretfully put myself in a situation whereby cocaine has been able to filter into my system through environmental contamination and must live with the consequences.
“As a professional sportsman I cannot put myself in a similar situation again.
“Even though I have been exonerated from taking cocaine, I would like to take this opportunity to apologise to Sheikh Fahad al Thani, David Redvers and Andrew Balding and thank them for their support.
“I also want to thank my legal team, particularly Florence Gaudilliere, who represented me in France but also Rory Mac Neice, the Professional Jockeys Association, Johnno Spence and others who have advised and supported me throughout.
“Finally, I would also like to apologise to the whole Qatar Racing team, to the owners and trainers I ride for, my supporters, my weighing room colleagues and to my commercial partners as well as Racing to School.
“The next three months will give me much time to reflect on my actions, but I will learn from this experience and come back better and even more determined than before.”
Backing from Balding
Balding, who handed Murphy his big breakthrough as an apprentice jockey, said: “Oisin Murphy arrived at Kingsclere in 2012 and is very much part of the Park House family. I have been very proud to watch him thrive in the saddle, but also as an ambassador for the sport.
“Oisin is a kind, trustworthy and dedicated part of the team. I never doubted he was innocent, but I know this will really hurt him and I will make sure we do everything to help him return as a stronger and better person.”
