Darya Klishina, 25, initially escaped a blanket ban on Russia's athletes for doping by governing body the IAAF, but her eligibility was revoked following new, but unspecified, information.
However, the Court of Arbitration for Sport has overturned that decision.
Qualifying for the long jump takes place on Tuesday.
"I can thankfully focus my time and attention on competing tomorrow night and enjoying my Olympic experience, which I have dreamed of since I first began long jumping as a young girl," said Klishina on Facebook.
Russian track and field athletes were banned from the Olympics following claims the country ran a state-sponsored doping programme.
Klishina, 10th in the 2015 World Championships, had been cleared to compete in her first Olympics as her drugs-testing record was established in the United States, where she is based, rather than in Russia.
In upholding Klishina's appeal, Cas said that her permanent residence outside Russia still applied despite the IAAF's additional information.
"We instigated a review process following new evidence presented to us," said the IAAF in response.
"The outcome we reached to revoke Darya Klishina's exceptional eligibility was not upheld by Cas despite the information received and she is therefore eligible to compete in Rio."
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The only Russian due to compete in the athletics at Rio 2016 has been cleared to contest the women's long jump after successfully appealing against a ban.