Lev Parnas and his business partner, Igor Fruman, had climbed to prominent places in the orbit of President Donald J. Trump when they were arrested at Dulles International Airport near Washington in 2019 while holding one-way tickets to Frankfurt.
The two Soviet-born businessmen were accused of funneling a Russian tycoon’s money into American political campaigns. But in the two years that followed, Mr. Parnas’s role in events connected to Mr. Trump’s first impeachment slowly emerged. He acknowledged participating in an effort by Rudolph W. Giuliani to pressure Ukrainian officials to investigate Joe Biden, who was then a leading Democratic presidential candidate.
Even as Mr. Parnas’s profile grew, though, the campaign finance charges against him loomed.
On Friday, in Federal District Court in Manhattan, Mr. Parnas and an associate, Andrey Kukushkin, were convicted on all counts. Mr. Fruman and a fourth defendant, David Correia, had pleaded guilty previously.
In a statement, Damian Williams, the U.S. attorney in Manhattan, said Mr. Parnas and Mr. Kukushkin had conspired to manipulate the American political system to enrich themselves.
“Campaign finance laws are designed to protect the integrity of our free and fair elections, unencumbered by foreign interests or influence,” Mr. Williams said. “Safeguarding those laws is essential to preserving the freedoms that Americans hold sacred.”
Speaking outside the courtroom after the verdict was announced, Mr. Parnas’s lawyer, Joseph A. Bondy, said his client planned to appeal and seek to have the conviction vacated.
Mr. Parnas, who is not in custody, sounded subdued as he spoke.
“I’ve never hid from nobody,” he said, while thanking his supporters. “I’ve always stood up and told the truth.”
The verdict came after only about five hours of deliberations, following testimony from, among others, a onetime finance director of a super PAC supporting Mr. Trump; an ex-chief of staff to a former Republican congressman from Texas; and the 2018 Republican candidate for governor of Nevada.
Prosecutors outlined a two-part scheme, saying Mr. Parnas had lied to the Federal Election Commission about certain campaign donations he had made and that he and Mr. Kukushkin had tried to gain favor among candidates with contributions tied to the Russian tycoon, Andrey Muraviev, with whom they were involved in a cannabis business.
“The purpose behind this conspiracy was influence buying,” a prosecutor, Hagan Cordell Scotten, said during closing arguments on Thursday, adding: “The voters would never know whose money was pouring into our elections.”
Throughout the trial, Mr. Bondy presented his client as an enterprising businessman who was a longtime proponent of legalizing marijuana and who also wanted to lead a company that would bring natural gas from the United States to Europe to help prevent a Russian “stranglehold” on energy.
Mr. Parnas had strayed beyond his area of business expertise, Mr. Bondy said, but had not “willfully” broken any laws. Instead, he argued, Mr. Parnas had been flummoxed by the intricacies of campaign finance rules.
“He was in well over his head,” Mr. Bondy said. “But he had some good ideas.”
Gerald B. Lefcourt, a lawyer for Mr. Kukushkin, said that his client, too, had lacked “criminal intent” and was not involved in making political donations. Mr. Lefcourt said Mr. Kukushkin had planned to start a legal cannabis business and believed that Mr. Parnas and Mr. Fruman were politically connected experts who could help him accomplish that.
Instead, Mr. Lefcourt said, the two had taken money meant for business expenses and used it to pay off debts and finance their lavish lifestyles, essentially swindling Mr. Kukushkin.
“They looked at him as unsophisticated and inexperienced — a rube,” Mr. Lefcourt said during his closing argument.
The charges against the men were based largely on documentation that included campaign contribution receipts, bank records and logs of WhatsApp messages exchanged by the main figures in the case.
Approached outside the courthouse on Friday, a man who served on the jury said the documents had made for a convincing case.
The man, who declined to give his name because of the controversy surrounding Mr. Parnas and the case, said that Mr. Bondy’s suggestion that his client had been ignorant of campaign finance laws was not convincing. That, the man said, was at least partly because prosecutors’ had shown that contributions attributed to Mr. Parnas required a sign-off that the donation’s source understood campaign finance regulations.
The evidence presented at trial helped fill out a picture of Mr. Parnas, who was born in Ukraine, grew up with humble roots in Brooklyn, worked his way into an upper echelon of Republican donors and became a key figure in the impeachment of an American president.
Prosecutors said records showed that a $325,000 donation to the super PAC backing Mr. Trump, America First Action, Inc. had been falsely reported as coming from a company started by Mr. Parnas and Mr. Fruman. In reality, the prosecutors said, the money came from a loan Mr. Fruman had taken out on a condo he owned.
In court papers, prosecutors said the purpose of the donation was to present the company, Global Energy Producers, as successful and to “obtain access to exclusive political events and gain influence with politicians.”
Prosecutors also introduced financial records that they said showed donations to the Nevada governor candidate, Adam Laxalt, and another Nevada Republican had been made with a credit card tied to a New York company controlled by Mr. Fruman’s brother. Records also showed that two companies owned by Mr. Muraviev had wired $500,000 apiece to the company in fall 2018.
Prosecutors pointed to several text message exchanges that they said revealed the purpose of the transfers. Among them was a message from Mr. Parnas’s assistant, who wrote to Mr. Kukushkin asking when “Adam Laxalt’s team” could expect two checks.
Mr. Kukushkin wrote back, saying: “the money was transferred ~ $1M to Lev & Igor’s company a long time ago to cover all the contributions as planned.”
Mr. Fruman replied with apparent exasperation, writing: “Andrey, what kind of mushroom did you eat today!?” “What are these discussions with our secretary???????”
The next day Mr. Parnas wrote to Mr. Fruman, Mr. Kukushkin and Mr. Muraviev: “I don’t want to discuss everything over text.”
That exchange was part of a trove of messages between Mr. Parnas, Mr. Fruman, Mr. Kukushkin, Mr. Muraviev and, occasionally, others.
The emoji-laden exchanges showed the four men discussing payments to Mr. Fruman’s brother’s company, plans to attend political rallies, “licensing in the key states” — an apparent reference to the cannabis business — and, occasionally, squabbles over money.
Mr. Parnas and Mr. Fruman shared pictures of themselves with political figures, including Mr. Trump, Mr. Giuliani and Ron DeSantis, the Republican candidate for governor in Florida at the time. The pictures seemed designed to present the two as being close to Mr. Trump as a way of convincing Mr. Kukushkin and Mr. Muraviev to finance their political activities.
After Mr. Kukushkin wrote that “our contributions are kind of way too much,” Mr. Parnas responded with a photo that showed him smiling broadly and standing with Ivanka Trump and Jared Kushner.
Mr. Parnas had been an ardent supporter of Mr. Trump’s, and while working with Mr. Giuliani in 2018 and 2019, he traveled to Kyiv to press officials there to investigate Mr. Biden’s son Hunter. He was also in regular touch with Yuriy Lutsenko, who, as Ukraine’s chief prosecutor at the time, was urging the removal of the U.S. ambassador in Kyiv.
Mr. Trump’s eventual decision to recall the ambassador, Marie L. Yovanovitch, was cited during his first impeachment and became central to a federal investigation into whether Mr. Giuliani broke lobbying laws.
By the time the trial began, Mr. Parnas had long since soured on Mr. Giuliani and Mr. Trump, saying he regretted ever trusting them.
In addition to providing material to the House Intelligence Committee as part of its impeachment inquiry, he made public a phone video from a small dinner in early 2018 at the Trump Hotel in Washington.
The video captured Mr. Parnas referring to Ms. Yovanovitch, saying she was a holdover from the Clinton administration who had been criticizing Mr. Trump — a claim the ambassador denied.
“Get rid of her,” Mr. Trump replied.
The following year, after Mr. Parnas was arrested, Mr. Trump denied knowing him.