The government had monitored Mr Page under the Foreign Intelligence Surveillance Act (FISA) and the heavily redacted documents were made public after media organisations sued for their release under the Freedom of Information Act.
The release of the document, along with three subsequent applications to renew the surveillance, was described as "extraordinary and historic".
In the four decades that FISA has been in effect, it's not clear that any application for surveillance has ever been released.
Materials related to FISA operations and legal process are among the most highly classified and closely guarded in the government.
The New York Times, USA Today, and the James Madison Project all sued for release of the materials.
It is expected to fuel the political fight between Republicans and Democrats over the propriety of the surveillance and how it was legally justified.
Republican lawmakers have accused the Obama administration, which sought the surveillance order in October 2016, of relying on a controversial dossier of then-candidate Donald Trump's alleged connections to Russia to support the surveillance order.
The document, compiled by a former British intelligence officer, was used as political opposition research by Democrats. But the author, Christopher Steele, also shared his findings with the FBI because he was concerned that Trump may have been compromised by Russia.
Members of the House Intelligence Committee have sparred for months over the Page surveillance.
Republicans, who previously released some details about the application, had accused the FBI of relying too much on the Steele dossier, which they painted as politically motivated and uncorroborated.
But Democrats countered that the FISA application relied on more information than what Mr Steele provided. And they said Mr Steele had been a reliable source of information to the FBI in the past.
On Saturday. California Democrat Adam Schiff, who sits on the House Intelligence Committee, said: “Even in redacted form, the initial FISA application and three renewals underscore the legitimate concern FBI had about Mr Page's activities as it was investigating Russia's interference,”
But, he added: “While I'm pleased that these conspiracy theories are finally being put to rest, the release of these materials during a pending investigation should not have happened,” referring to the ongoing probe of Russian interference in the US elections.
The application shows that the FBI portrayed Mr Steele to the court as a trusted source.
The FBI also disclosed that his work was on behalf of a client who was likely looking for politically damaging information about Trump.
Republicans had accused the bureau of failing to notify the court of the dossier's political origins.
Much of the more than 400 pages of applications is redacted, making it impossible to know all the evidence that the FBI presented to a judge in seeking the wiretap order.
In particular, whole sections in the application detailing the FBI's justification for believing Mr Page was a Russian agent are blacked out. Some of the unredacted material refers to news articles.
But FISA applications typically rely on classified and other sensitive information, according to officials with knowledge of the process.
The application identifies Mr Page by name and says that he engaged in “clandestine intelligence activities” on behalf of Russia and had been the target of Russian government recruitment.
The application describes Russia as having interfered in the 2016 presidential election.
Mr Page has denied that he was a Russian agent.
The Washington Post
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