New Jersey Senator Bob Menendez has been found guilty on 16 counts tied to a scheme where he accepted bribes, including gold bars and a Mercedes-Benz, in exchange for helping foreign governments.
A jury convicted Menendez of all charges after more than 12 hours of deliberation over three days. The trial lasted nine weeks.
Menendez - formerly the head of the powerful Senate Foreign Relations Committee - now faces the prospect of decades in prison.
Democratic lawmakers have called on him to step down from Congress in light of his conviction.
"Senator Menendez must now do what is right for his constituents, the Senate, and our country, and resign," said Democratic Senate Majority leader Chuck Schumer in a statement.
Speaking to reporters after his conviction, Menendez maintained that he is innocent.
"I never violated my public oath," he said outside the New York City courthouse on Tuesday. "I have never been but a patriot of my country and for my country."
His lawyer, Adam Fee, said that he was "surprised and disappointed" with the jury's guilty verdict and has vowed to appeal "aggressively."
Prosecutors said the case represented "shocking levels of corruption."
"This wasn't politics as usual, this was politics for profit," said Damian Williams, an attorney for the Southern District of New York.
"Now that the jury has convicted Bob Menendez, his years of selling his office to the highest bidder have finally come to an end," Williams said.
Menendez pleaded not guilty in the trial. His lawyers argued that the gifts he accepted did not qualify as bribes, because prosecutors had failed to prove that he took any specific action as a result of receiving them.
His wife, Nadine Arslanian Menendez, also faces charges in the bribery case, but her trial was delayed so she could undergo breast cancer treatment. She has pleaded not guilty.
His lawyers had attempted to shift blame to Mrs Menendez, portraying her as a financially troubled individual who hoped to "get cash and assets any way she could".
Meanwhile, prosecutors relied on expert testimony, emails and Menendez's text messages to show that the senator accepted lavish rewards from foreign governments.
They said the gifts included gold bars worth over US$100,000. Some of the bars were handed to jurors as evidence in the trial.
Jurors also heard that FBI agents had found more than US$480,000 in cash inside of Menendez's home, some of which was stuffed in envelopes and coats.
Two businessmen, Wael Hana and Fred Daibes, are also being tried on accusations that they sought out the senator to illegally aid the Egyptian government and secure millions of dollars from a Qatari investment fund.
A third businessman, Jose Uribe, pleaded guilty and testified against Menendez in the trial.
In exchange the bribes, prosecutors said Menendez helped secure millions of dollars in US aid for Egypt, where Hana had ties to government officials.
He was also accused of trying to influence criminal probes involving Daibes and Uribe. Both businessmen were co-defendants in Menendez's case and were also convicted on the counts they faced.
Menendez is currently running as an independent as he campaigns to keep his seat in November's election. Most Democrats in the state walked away from him last year after the release of the indictment showing gold bars stashed in his home.
Andy Kim, a Democratic congressman from New Jersey, said the verdict marked "a sad and sombre day" for his state.
"I called on Senator Menendez to step down when these charges were first made public, and now that he has been found guilty, I believe the only course of action for him is to resign his seat immediately," Kim said in a statement.
"The people of New Jersey deserve better," he said.
The senator has faced federal corruption charges before. He was tried in 2017, with the justice department alleging he did political favours for a wealthy Florida eye doctor in exchange for luxury holidays and other lavish gifts.
But that case ended in a mistrial after he was acquitted on some charges and jurors were unable to reach a unanimous verdict.
- BBC