A federal appeals court said Tuesday that Deutsche Bank must turn over detailed documents about President Trump’s finances to two congressional committees, a ruling that is almost certain to be appealed to the Supreme Court.

The decision was a victory for House Democrats as they investigate Mr. Trump and his businesses. It means that extensive information about Mr. Trump’s personal and business finances — which the president has spent years fighting to keep secret — has moved a step closer to becoming public.

Democratic-controlled congressional committees issued subpoenas to two banks — Deutsche Bank, long Mr. Trump’s biggest lender, and Capital One — this year for financial records related to the president, his companies and his family. Mr. Trump sued the banks to block them from complying.

Mr. Trump’s lawyer didn’t immediately respond to a request for comment. The court’s ruling gave Mr. Trump seven days to appeal the decision.

Deutsche Bank became Mr. Trump’s main lender after a string of bankruptcies cost other banks hundreds of millions of dollars, and its files would most likely contain a rich trove of documents including details about how he made his money, who his partners have been, the terms of his extensive borrowings and other transactions.

Investigators for the two committees are hoping the materials will also shed light on any links he has had to foreign governments and whether he or his companies were involved in any illegal activity, such as money laundering for people overseas.

The ruling by the United States Court of Appeals for the Second Circuit contained one caveat: The lower court must consider whether and how the banks disclose a limited set of sensitive personal information to Congress that would have no bearing on government investigations. That includes items such as checks that were written by Mr. Trump or his companies to cover employees’ medical expenses.

But, the court ruled, the presumption should be in favor of handing over more documents, not fewer. “Many documents facially appearing to reflect normal business dealings will therefore warrant disclosure for examination and analysis by skilled investigators assisting the committees to determine the effectiveness of current regulation and the possible need for improved legislation,” the court wrote.

The ruling concluded: “The committees’ interests in pursuing their constitutional legislative function is a far more significant public interest than whatever public interest inheres in avoiding the risk of a Chief Executive’s distraction arising from disclosure of documents reflecting his private financial transactions.”