Attempts to reach Mr. Gates on Monday were unsuccessful.

If convicted of money laundering, the most serious charge, Mr. Gates and Mr. Manafort could face up to 20 years in prison.

Mr. Manafort had been under federal investigation on suspicion of violating tax law, laundering money and whether he appropriately disclosed his foreign lobbying work. As Mr. Manafort’s business associate, Mr. Gates’s name is listed on documents that are linked to companies Mr. Manafort’s firm established in Cyprus for payments from politicians and businesspeople in Eastern Europe, according to records reviewed by The New York Times.

When the business partners worked in Ukraine, Mr. Gates flew to Moscow for meetings with associates of a Russian oligarch, Oleg Deripaska.

Mr. Gates and Mr. Manafort met years ago when Mr. Gates was interning at Mr. Manafort’s Washington consulting firm, Black, Manafort, Stone, Kelly. The firm was known for running Republican political campaigns and then lobbying the politicians after they won their elections.

In Washington, Mr. Manafort was known for representing dictators and strongmen, such as Ferdinand Marcos of the Philippines. Mr. Manafort also represented the Trump Organization to lobby the Treasury Department regarding casino transaction rules.

Mr. Gates would later follow Mr. Manafort to a new firm, Davis Manafort, which worked on the campaign of Viktor F. Yanukovych, the pro-Russia former Ukranian president. This work connected the men with Mr. Deripaska, an aluminum magnate and ally of President Vladimir V. Putin of Russia. Mr. Deripaska has been denied a visa to travel to the United States because of allegations that he is linked to organized crime operations, charges Mr. Deripaska has denied.

In 2008, Mr. Gates took over the firm’s duties in Eastern Europe, where he worked on business development and contract negotiations.