* Most prominent former Trump aide to plead guilty
* Manafort ran campaign at key 2016 moments US President Donald Trump's former campaign chairman Paul Manafort will cooperate with Special Counsel Robert Mueller's probe of Russian election meddling as part of a plea deal, prosecutors told a federal court in Washington on Friday.
Manafort, 69, also pleaded guilty to two criminal counts, becoming the most prominent former Trump campaign official to plead guilty in Mueller's investigation.
The probe has cast a shadow over the Republican's presidency and Manafort's decision to cooperate deals a setback to Trump ahead of congressional elections on November 6.
A longtime Republican operative, Manafort made millions of dollars working for pro-Russian Ukrainian politicians before taking an unpaid position with Trump's campaign for five months.
He led the campaign in mid-2016 when Trump was selected as the Republican presidential nominee at the party convention.
Moscow has denied interfering in the 2016 election and Trump has said there was no collusion.
Manafort on Friday pleaded guilty to one count of conspiracy against the United States and one count of conspiracy to obstruct justice brought by Mueller's team. Other counts were dropped.
Before Manafort's appearance, there was some discussion that he would plead guilty without cooperating and perhaps later receive a presidential pardon. Trump had not said he would pardon Manafort, but nor had he ruled it out.
Rudy Giuliani, the former New York City mayor who is now representing Trump in the Russia probe, told Reuters on Friday before the hearing that a guilty plea would not crush Manafort's chances of receiving an eventual presidential pardon.
"It’s not going to hurt him if he pleads guilty. Usually it helps you get a pardon down the road. It shows you’ve admitted your guilt," he said before the deal was announced. He declined further comment until after the hearing.
Manafort made millions of dollars working for pro-Russian Ukrainian politicians before taking an unpaid position with Trump's campaign for five months. He led the campaign in mid-2016 when Trump was selected as the Republican presidential nominee at the party convention.
Moscow has denied interfering in the 2016 election and Trump has said there was no collusion.
Guilty plea
A Virginia jury convicted Manafort last month on bank and tax fraud charges. Prosecutors had accused him of hiding from US tax authorities $16mn he earned as a political consultant in Ukraine to fund an opulent lifestyle and then lying to banks to secure $20mn in loans.
The jury in that case deadlocked on 10 counts that on Friday were dropped as part of the plea deal.
Jury selection was due to begin on Monday in a second Manafort trial on charges including conspiring to launder money, conspiring to defraud the United States, failing to register as a foreign agent and witness tampering.
Trump last month praised his former aide for not entering into an agreement with prosecutors, as the president's former personal lawyer Michael Cohen had.
On Twitter on August 22, Trump wrote: "Unlike Michael Cohen, he refused to 'break' - make up stories in order to get a 'deal. Such respect for a brave man!"
