A major donor to both Donald Trump and Hillary Clinton made hundreds of thousands of dollars of illegal campaign contributions, some from foreign sources, to help cultivate influential U.S. politicians, according to charging documents filed Tuesday by federal prosecutors in California.

California businessman Imaad Zuberi, 49 years old, capitalized on his access to U.S. politicians to drum up business from foreign governments and foreign individuals, whom he later defrauded as part of a scheme to enrich himself, prosecutors say.

Mr. Zuberi will plead guilty to making illegal campaign contributions, tax evasion and falsifying lobbying records to conceal his work for foreign governments, according to charging documents filed in federal court in Los Angeles on Tuesday. He faces a maximum of 15 years in prison, though first-time offenders rarely receive the maximum sentence.

“Mr. Zuberi’s multifaceted scheme allowed him to line his pockets by concealing the fact that he was representing foreign clients, obtaining access for clients by making a long series of illegal contributions, and skimming money paid by his clients,” said Nick Hanna, the U.S. attorney in Los Angeles. “Mr. Zuberi circumvented laws designed to insulate U.S. policy and our election process from foreign intervention,” he said.

Mr. Zuberi’s attorney didn’t respond to a request for comment.

“The Zuberi prosecution is one of the largest campaign-finance prosecutions in recent memory—a sprawling indictment touching most major areas of campaign finance law—from straw donors to corporate contributions to foreign nationals,” said David Mitrani, an election law attorney at the firm Sandler Reiff. “Prosecutors and the Department of Justice are watching these issues very closely.”