Patten pleaded guilty before U.S. District Court Judge Amy Berman Jackson, who will also be hearing a case against Manafort starting September 24 involving charges of money laundering and failing to file as a foreign agent.
The charges are spelled out in a criminal information, which often precedes a guilty plea.
In the early to mid-2000s, Patten worked in Moscow for another pro-democracy organization, the International Republican Institute, along with Konstantin Kilimnik, who has been charged by Mueller's office with obstruction of justice and conspiracy to obstruct justice.
Patten's plea agreement, which includes cooperating with Mueller, raises the prospect Patten will be called to testify against Manafort, who was found guilty by a Virginia jury last week on bank and tax fraud charges and faces a second trial in Washington next month.
Kilimnik is charged alongside Manafort in a separate criminal case brought in Washington by Mueller.
Patten allegedly worked to set up meetings for Kilimnik and the Ukrainian oligarch with state department officials and members of Congress, including senators on the foreign relations committee and House members on the foreign affairs committee.
Laws requiring lobbyists to register if they lobby in the United States on behalf of foreign governments and political parties have been loosely enforced for years.
Prosecutors describe Foreigner A as a "Russian national" who partnered with Patten to create a political consulting company, "Company A", split 50-50.
The charge, brought by the U.S. Attorney's office, stemmed from information uncovered by special counsel Robert S. Mueller III's investigation into possible ties between the 2016 Trump campaign and Russian Federation.
The charges he pleaded guilty to are failing to register his work as a foreign agent while doing work in Washington for a Ukrainian political party.
Manafort made most of his money working for former Ukrainian President Viktor Yanukovych before he fled to Russian Federation in 2014, but like Patten also sought to drum up business with the Opposition Bloc in the aftermath of Yanukovych's exit.
In court, Patten conveyed the air of a solemn man aware of what he had done. The funds were allegedly paid via an offshore account in Cyprus from a "prominent Ukraine oligarch" who is an Opposition Bloc member.
Samuel Patten, 47, also agreed to cooperate with Mueller's probe.
The charges against Patten were filed by the US attorney's office in Washington rather than by Mueller.
Patten was released on his own recognizance but can not travel outside the Washington area without notifying the court.
But with Manafort's prosecution, the Justice Department has been more closely scrutinizing such work.
Beyond his work as a translator, Patten told The Post that Kilimnik would "help Manafort understand the political context and why people were doing what they were doing".
Court papers say the op-ed was published in February 2017 in a "national United States media outlet", but they do not name the media outlet or Foreigner B. However, on February 6, 2017, an op-ed published under Serhiy Lyovochkin's name appeared in U.S. News and World Report.