A federal appeals court overturned the conviction of former Representative Jeff Fortenberry, a Nebraska Republican, on Tuesday, ruling that his trial should not have taken place in Los Angeles.

Mr. Fortenberry, 62, was convicted in March 2022 on three felony charges related to lying to federal authorities about illegal campaign donations he received at a 2016 fund-raiser in Los Angeles.

He had told federal investigators during interviews at his home in Nebraska and his lawyer’s office in Washington, D.C. that he did not know about the origin of $30,000 in donations from a Lebanese Nigerian billionaire, Gilbert Chagoury, who was ineligible to contribute to an American candidate. However, an F.B.I. agent had previously heard a phone call in which a cooperating witness informed the congressman about the source of the funds.

The three-judge panel determined that Mr. Fortenberry should not have been tried in Los Angeles because he made his statements about the campaign contributions in Nebraska and Washington, D.C. He was charged and convicted of making false statements, not the receipt of the illegal contributions.

“The constitution plainly requires that a criminal defendant be tried in the place where the criminal conduct occurred,” Judge James Donato wrote on behalf of the United States Court of Appeals for the Ninth Circuit.

The court said Mr. Fortenberry could be retried in a proper venue.

Thom Mrozek, a spokesman for the U.S. Attorney’s Office in Los Angeles, said in a statement that a retrial was possible.

“We are evaluating potential next steps before deciding how best to move forward,” he said.

In a statement provided by his lawyer, Mr. Fortenberry said on behalf of himself and his wife: “We are gratified by the Ninth Circuit’s decision. Celeste and I would like to thank everyone who has stood by us and supported us with their kindness and friendship.”

Mr. Fortenberry, who was first elected to Congress in 2004, resigned days after his conviction. He had been urged to do so by Nebraska’s Republican governor and by colleagues from both parties, including Representative Kevin McCarthy, who was the minority leader, and Representative Nancy Pelosi, who was the House speaker.

In June 2022, Mr. Fortenberry was sentenced to two years of probation and was ordered to pay a $25,000 fine and perform 320 hours of community service.

The Nigerian billionaire in question, Gilbert Chagoury, has paid $1.8 million in fines to the U.S. government for making improper donations to several campaigns.