WASHINGTON — Representative Jeff Fortenberry, Republican of Nebraska, announced on Saturday that he would resign from Congress at the end of the month, days after he was convicted on charges that he lied to federal authorities about an illegal campaign donation.

Mr. Fortenberry, in a letter to his colleagues, said he would step down from his seat on March 31. On Thursday, he was convicted on three felony counts in a federal court in Los Angeles, including two counts of making false statements and one count of falsifying and concealing material facts.

He faces a maximum sentence of five years in prison for each count, according to the Justice Department, and a sentencing hearing is scheduled for the end of June. And while Mr. Fortenberry has said he plans to appeal the decision, national and local leaders in both parties called for his resignation in the aftermath of the verdict, including Representative Kevin McCarthy of California, the House minority leader, and Speaker Nancy Pelosi of California.

“It has been my honor to serve with you in the United States House of Representatives,” Mr. Fortenberry wrote. “Due to the difficulties of my current circumstances, I can no longer effectively serve.”

In a newsletter sent to his constituents, he added, “It is my sincerest hope that I have made a contribution to the betterment of America and the well-being of our great state of Nebraska.”

Mr. Fortenberry, who was first elected to Congress in 2004, had already given up his committee positions, including a seat on the powerful House Appropriations Committee, under Republican conference rules for members facing federal indictments.

“He had his day in court — I think if he wants to appeal, he can go do that as a private citizen,” Mr. McCarthy said after the verdict was announced. “When someone’s convicted, it’s time to resign.”

The charges came after Mr. Fortenberry denied knowledge that he had received $30,000 in donations at a 2016 campaign fund-raiser in Los Angeles from Gilbert Chagoury, a Lebanese Nigerian billionaire, who had been accused of conspiring to make illegal donations to American politicians. (Foreign citizens cannot donate to American election campaigns, and Mr. Chagoury has since paid a $1.8 million fine after a deal with the U.S. government.)

Mr. Chagoury had funneled the donation through an intermediary, according to the indictment. But prosecutors said that despite being told by a cooperating witness who helped transfer the money to his campaign that the donations “probably did come from Gilbert Chagoury,” Mr. Fortenberry denied knowing that the money had come from a foreign citizen.

He was first interviewed by federal investigators in 2019, as part of an inquiry into Mr. Chagoury’s donations to multiple candidates between 2012 and 2016. Mr. Fortenberry was indicted in October, and he was convicted this week after a weeklong trial.