In a newly-released sentencing memo, Mr Mueller’s team said: “Given the breadth of Manafort’s criminal activity, the government has not located a comparable case with the unique array of crimes and aggravating factors.”
The document also revealed Manafort continued to break the law even after his 2017 indictment by the special prosecutor, who is investigating Russian election interference and related matters.
“For over a decade, Manafort repeatedly and brazenly violated the law,” the memo states.
“His crimes continued up through the time he was first indicted in October 2017 and remarkably went unabated even after indictment.”
The 25-page memo – filed with over 800 pages of notes in a federal court in Washington – is likely to be the last major filing by special prosecutors as Manafort heads into his sentencing hearings next month and as Mr Mueller’s investigation approaches a conclusion.
The document depicts Manafort as an unrepentant criminal who committed “bold” financial crimes and lied to the FBI, government agencies and even his own lawyer.
It said: “Manafort chose repeatedly and knowingly to violate the law – whether the laws proscribed garden-variety crimes such as tax fraud, money laundering, obstruction of justice, and bank fraud, or more esoteric laws that he nevertheless was intimately familiar with, such as the Foreign Agents Registration Act (FARA).”
FARA requires acting on behalf of a foreign country to disclose the nature of the work. Manafort failed to register his lobbying efforts for Ukraine in 2007, despite having previously been caught failing to register his work for Saudi Arabia between 1984 and 1986.
“His criminal actions were bold, some of which were committed while under a spotlight due to his work as the campaign chairman and, later, while he was on bail from this court,” said the filing.
In September Manafort pleaded guilty to two counts of conspiracy arising from his Ukrainian political consulting work and his efforts to tamper with witnesses. As part of that plea, he agreed to cooperate with Mr Mueller’s team, a move that could have helped him avoid a longer prison sentence.
But within weeks, prosecutors say he repeatedly lied to investigators, including about his interactions with Konstantin Kilimnik, a business associate who the US says has ties to Russian intelligence. That deception ended the plea deal.
In recent weeks, court papers have revealed that Manafort shared polling data related to the Trump campaign with Mr Kilimnik. A Mueller prosecutor also said earlier this month that an August 2016 meeting between Manafort and Mr Kilimnik goes to the “heart” of the Russia probe.
The meeting involved a discussion of a Ukrainian peace plan, but prosecutors have not said exactly what has captured their attention and whether it factors into Russia’s attempts to help Donald Trump in the 2016 election.
Mr Mueller’s team urged a US judge not to consider any mitigating factors in sentencing the former Trump campaign chairman, increasing the likelihood Manafort will spend the rest of his life in jail.
The special counsel’s prosecutors have not yet taken a position on how much prison time he should serve, or whether the prison sentence in the Washington case related his Ukrainian political consulting work should run consecutively with a separate punishment that Manafort faces in a bank and tax fraud case in Virginia.
Mr Mueller’s team has endorsed a sentence of between 19.5 and 24.5 years in prison in the Virginia case. Prosecutors said in the latest memo that “upon release from jail, Manafort presents a grave risk" of reoffending.
Manafort, who turns 70 in April, will have a chance to file his own sentencing recommendation next week.
Additional reporting by agencies