The two-time Olympic gold medalist had been held in a Russian jail on drugs charges.
US basketball star Brittney Griner was released from a Russian prison on Thursday in a dramatic high-level prisoner exchange with an arms dealer nicknamed the "Merchant of Death."
American officials said two-time Olympic gold medalist Griner was swapped with Russian arms dealer Viktor Bout.
The swap, at a time of heightened tensions over Ukraine, achieved a top goal for President Joe Biden, but carried a heavy price -- and left behind an American jailed for nearly four years in Russia.
In a live address, US President Joe Biden said he had spoken to Griner on the phone.
"She's safe, she's on a plane, she's on her way home after months of being unjustly detained in Russia, held under intolerable circumstances. Brittney will soon be back in the arms of her loved ones, and she should have been there all along," Biden said, standing beside Griner's wife Cherelle.
Biden added that Griner would be back in the US "in the next 24 hours".
Cherelle Griner said the last nine months had been some of the darkest moments of her life, "so today I'm just standing here overwhelmed with emotions. But the most important emotion I have right now is just sincere gratitude," she said, before thanking Biden and US government officials, her friends and family and the WNBA organisation.
The deal, the second such exchange in eight months with Russia, procured the release of the most prominent American detained abroad. Griner was imprisoned on drug charges and brought unprecedented attention to the population of wrongful detainees.
Biden's authorisation to release Bout underscored the escalating pressure that his administration faced to get Griner home, particularly after the recent resolution of her criminal case and her subsequent transfer to a penal colony.
Russian and US officials had conveyed cautious optimism in recent weeks after months of strained negotiations, with Biden saying in November that he was hopeful that Russia would engage in a deal now that the midterm elections were completed. A top Russian official said last week that a deal was possible before the year's end.
Griner freed but another American remains in Russian jail
The fact that Brittney Griner was released in a one-for-one swap was a surprise given that US officials had for months expressed their determination to bring home both Griner and Paul Whelan.
Whelan is a corporate security executive jailed in Russia since December 2018 on espionage charges that his family and the US government have said are baseless.
In releasing Bout, the US freed a former Soviet Army lieutenant colonel whom the Justice Department once described as one of the world's most prolific arms dealers. Bout, whose exploits inspired a Hollywood movie, was serving a 25-year sentence on charges that he conspired to sell tens of millions of dollars in weapons that US officials said were to be used against Americans.
The Biden administration was ultimately willing to exchange Bout if it meant Griner's freedom. The detention of one of the greatest players in WNBA history contributed to a swirl of unprecedented public attention for an individual detainee case -- not to mention intense pressure on the White House.