Patten has no prior criminal history, his plea agreement said.
The Justice Department alleges that between 2014 and 2018, Patten acted on behalf of the Ukrainian political party, Opposition Bloc, a Russia-allied political group.
Facing up to five years in federal prison and a $250,000 fine, Patten pleaded guilty on Friday and agreed to cooperate with prosecutors according to the terms of his plea deal. The special counsel office believes Kilimnik has strong ties with Russian intelligence officials.
Prosecutors alleged in the charging document filed in court Friday that Patten violated the law starting in January 2015 when he and "Foreigner A" began reaching out to members of Congress, White House officials, and media publications to set up meetings with his client, "Foreigner B". The document said he did not register as a foreign agent with the State Department under the Foreign Agent Registration Act (FARA) while doing his political consulting work.
The charges are spelled out in a criminal information, which often precedes a guilty plea. The unidentified oligarch was one of their biggest benefactors, the charging documents said.
Patten formed a consulting company in the US with Konstantin Kilimnik, a Russian political operative with alleged ties to the country's intelligence services. The client wasn't eligible to buy the tickets themselves because the inauguration committee couldn't accept foreign money under Federal Election Commission rules.
In a 2017 interview with an academic researching SCL Group, Patten reflected on his experience in worldwide political consulting and said, "I've worked in Ukraine, Iraq". The two set up the political advisory firm Begemot Ventures Ltd LLC in February 2015, which was paid more than $1 million for their work for Ukrainian interests.
That alarmed allies of Petro Poroshenko, Ukraine's president, who is generally regarded as more pro-Western, and it emboldened his pro-Russian opponents, who had held power from 2010 to 2014 partly through the efforts of Manafort and his former right-hand man, Rick Gates.
Kilimnik has been indicted in absentia alongside Manafort on obstruction of justice charges. Kilimnik also is a co-defendant in a pending case against Manafort in Washington, brought by special counsel Robert Mueller's team, that accuses them both of witness tampering.
Manafort's relationship with Kilimnik stretches back years.
Manafort's name was not mentioned once during Friday's hearing.
Talks of President Donald Trump pardoning Paul Manafort, in an effort to disrupt Mueller's Russian Federation probe, have prompted even Trump loyalists, who reportedly claim that Trump's pardoning of Paul Manafort would be a "bridge too far", to caution the POTUS, according to Alternet. Last year, it also emerged that Manafort emailed Kilimnik in 2016 offering to give Deripaska "private briefings" about the campaign.
Manafort, who was sacked as Trump's campaign chairman in August 2016, was convicted by a federal jury in Virginia on tax and bank fraud stemming from his work between 2010 and 2014 for the pro-Russia Ukrainian political party Party of Regions and then-President Viktor Yanukovych.