"I am sorry for what I have done and for all the activities that have gotten us here today", Manafort told the judge.
During the same hearing, the judge also appeared to allude to another possible interaction at the Havana Room gathering: a handoff by Manafort of internal polling data from Trump's presidential campaign to his Russian associate.
The charges include 16 counts of state felonies, which would put Manafort behind bars for up to an additional two decades if convicted. The president has called Manafort courageous for fighting his case against special counsel Robert Mueller, who is investigating Russian interference in the 2016 election.
Jackson slammed Manafort for his crimes, which stemmed back years to when he lobbied and consulted for pro-Russian politicians in Ukraine.
Manafort's lawyers have noted that the charges that are sending him to prison are related to his work as an global political consultant and lobbyist, not his time with the Trump campaign.
Jackson said she read all the letters before determining his sentence.
Jackson also harshly criticized Manafort for years of deception that extended even into her own courtroom and the grand jury.
Once a globe-trotting political operative who helped elect President Trump and three of his Republican predecessors, Manafort returned to federal court as a felon apologizing for his criminal conduct in the hard fall from his power-broker days. He pleaded with the judge not to impose any additional time beyond the sentence he had received last week in a separate case in Virginia. After he pled guilty, he said, Manafort then lied to the Federal Bureau of Investigation and a grand jury even though he had agreed to cooperate.
The judge ruled earlier this year that Manafort breached his plea deal by lying to the Federal Bureau of Investigation, prosecutors and grand jurors during more than 50 hours of interviews.
Manafort's attorneys nonetheless argued that he had shown contrition by admitting guilt and that he has been struggling against an unfair and incorrect portrayal of himself in the press.
Last week, in a federal court in Virginia, Manafort was sentenced to almost four years in prison (47 months) in a separate case, involving bank and tax fraud. His lawyers suggested that Manafort only faced conspiracy charges because Mueller couldn't charge him with anything related to collusion.
Manafort was being sentenced for concealing from the government foreign lobbying work.
Speaking to reporters after the sentencing, Manafort's attorney Kevin Downing said Jackson exhibited callousness that was "hostile and totally unnecessary".
Manafort's lawyers used court papers to be critical of Mueller's investigation and the lack of charges related to the 2016 presidential election.
He undermined the American political process by concealing from the public and Congress that he was working on behalf of Ukraine- and earning millions of dollars that he never reported to the IRS, she said.
The Atlantic's Natasha Bertrand (an MSNBC contributor) tweeted that Kevin Downing, one of Manafort's lawyers, "is saying that Judge ABJ found that there was no evidence of Russian Federation collusion" and that protestors responded, "That's not what she said".