A D.C. businessman at the center of a far-reaching corruption probe into Mayor Vincent C. Gray’s 2010 campaign must let prosecutors pore through millions of pages of personal and business records, a federal appeals court ruled Tuesday.

Jeffrey E. Thompson, who is alleged to have financed a “shadow campaign” for Gray (D) that was not disclosed as required by election laws, had fought to keep federal investigators from seeing some of the documents. It is unclear what the documents contain, but prosecutors have fought eagerly to get them to help with their investigation.

The ruling, by the U.S. Court of Appeals for the District of Columbia Circuit, was kept under seal Tuesday, but it was confirmed by two people familiar with its content. In addition, the court’s online docket showed Tuesday that Thompson’s appeal had been dismissed. A lower court ruling last May first disclosed the haul of more than 60 boxes of records and the request by Thompson’s attorney to narrow the review of the documents.

The records under dispute were seized, at least in part, during federal raids at Thompson’s home and offices last March, and a large chunk of them have been in legal limbo ever since.

Federal officials at the time said the raids were part of an investigation into city corruption, and one of Thompson’s accounting partners told city officials that the search pertained to Thompson’s campaign-finance activities. The raid prompted close media scrutiny of Thompson’s campaign donations in the District and elsewhere.

But the scope of his potential involvement in corrupt activities was not revealed until July, when a former associate, Jeanne Clarke Harris, pleaded guilty in federal court to helping orchestrate the shadow campaign in support of Gray during the 2010 mayoral election. Several people familiar with the investigation said that Thompson was the “co-conspirator” named in court filings who funded the secret, $653,000 effort.

U.S. Attorney Ronald C. Machen said at the time that the mayoral race was “compromised by backroom deals, secret payments and a flood of unreported cash.”

Under city campaign finance laws, all contributions and expenditures made on behalf of a candidate must be publicly reported. But as part of the Harris case, prosecutors alleged that Thompson wanted to keep his doings secret in order to protect his business interests with the city government if Gray were to lose.

Thompson’s health-care firm, Chartered Health Plan, did $355 million of business with the city in 2011. His accounting firm, Thompson, Cobb, Bazilio & Associates, did tens of millions more.

Since the raids, Thompson has sold his interest in the accounting firm and has withdrawn from the management of Chartered, which is now under city receivership and on the cusp of liquidation.

Prior to the raids a year ago, Thompson was a prolific fundraiser for candidates both in the city and elsewhere. Prior to his alleged secret support of Gray, he was a close supporter of former mayor Anthony A. Williams (D), and he also gave to Williams’s successor, Adrian M. Fenty. Thompson also has raised funds, to various degrees, for a majority of D.C. Council members, Martin O’Malley’s successful 2010 Maryland governor campaign and Hillary Rodham Clinton’s 2008 presidential run.

In the earlier opinion, U.S. District Judge Royce C. Lamberth wrote that some of the documents were protected by various privileges, such as the attorney-client privilege.

But Lamberth rejected Thompson’s argument that his attorneys should be allowed to review the records first. Lamberth said he had confidence in the U.S. attorney’s ability to set up an independent filtering team to review records that might contain privileged information.

Thompson’s attorney, Brendan Sullivan, said Tuesday, “We do not comment about cases.”

A spokesman for the U.S. attorney’s office also declined to comment.