He wrote on Twitter: "In the back of the Spanish police auto going to the station on the Russian arrest warrant, they won't tell me which station".
Later, Browder posted another tweet, informing on his release: "Good news".
He later tweeted out what he said was an image of the warrant.
The financier, who is a plaintiff in the Spanish investigation, said Spain is among 15 countries following the money trail.
Spanish law enforcement said officers let Browder go after it was "verified by INTERPOL Spain that the arrest warrant issued by the Russian authorities for tax evasion was invalid". "Agents have confirmed that this warrant/order is no longer valid and he has been freed".
The U.S. -born businessman said in a tweet he had been arrested in the Spanish capital. He was once the largest investor in Russia's stock market and a supporter of the Russian President.
Browder claims his expulsion was because of his criticism of Russian corporate governance. The UK does not have an extradition treaty with Russian Federation, which was fortunate for Browder.
Browder's lawyer, Sergei Magnitsky, was put in pretrial detention, tortured, and killed in Russian custody in 2009.
A Home Office minister called it an "atrocious murder" and it led to calls for the Magnitsky amendment, enabling the government to freeze the United Kingdom assets of those suspected of abusing human rights, which was recently approved by the Commons. "They won't tell me which station", Browder said in a tweet, which include a photo taken from the back of a police auto.
"While Russia has "repeatedly repeatedly requested Mr. Browder's arrest through Interpol", The New York Times reports, ". its requests have been refused repeatedly.
Browder has previously claimed that Putin has tried multiple times to use Interpol, the multinational police organization, to target him overseas. "Each request has been summarily rejected, including the most recent".
Two years ago Interpol appointed a senior figure from Vladimir Putin's administration as vice president for Europe.
British Foreign Minister Boris Johnson said he spoke to Mr Browder and was "very glad that he has now been released".
Moscow's Tverskoy District Court earlier found Browder guilty in absentia of large-scale tax evasion estimated at more than three bln rubles ($48 mln) and sentenced him to nine years in prison.