The former American soccer official Chuck Blazer was providing information to federal prosecutors looking into corruption in world soccer’s governing body for nearly a year and a half while still a member of FIFA’s ruling executive committee, according to a plea agreement unsealed by a federal judge Monday.

The agreement was ordered released in United States District Court in Brooklyn by Judge Raymond J. Dearie, who said that prosecutors had not met the “high burden” to keep it under seal. It was dated Nov. 25, 2013, the same day Blazer pleaded guilty in a locked federal courtroom in Brooklyn to 10 counts of racketeering, wire fraud, money laundering and tax evasion. Judge Dearie released a transcript of that hearing June 3. The documents unsealed Monday outlined not only the terms of Mr. Blazer’s plea agreement, but also new details on his cooperation with the authorities.

Among the details disclosed was that Mr. Blazer secretly cooperated with federal investigators for nearly two years before his guilty plea — starting as early as December 2011 — and that he agreed to provide information and documents, to testify at trial upon request, and not to reveal his cooperation.

The plea agreement also confirmed that Mr. Blazer had agreed to work undercover for prosecutors. The Daily News had reported last fall that that cooperation had included taping conversations with other top soccer officials at the 2012 London Olympics.