Washington (CNN) Rick Gates, one of the most significant cooperators of the Mueller investigation, is poised to testify publicly against two of his former associates and potentially speak about the Trump campaign's interest in WikiLeaks and the Russian hack of the Democrats in 2016 before he is sentenced in the coming months.

Prosecutors and Gates' defense team filed a notice with the federal court in Washington Thursday night that Gates will be ready for sentencing about two years after his indictment.

The notice is the surest sign yet that federal authorities have wrapped major investigatory matters related to the 2016 Trump campaign.

But first, the former Trump deputy campaign chairman may have revealing details to share during the trial of Trump adviser Roger Stone in November.

Gates is also expected to be a witness in the upcoming trials of former Obama White House counsel Greg Craig and New York State's case against former Trump campaign chairman Paul Manafort.

The delay of Gates' sentencing since his October 2017 indictment had long been an indication that investigations into the Trump political operation and Russian-Ukrainian influence in American politics continued. The end of his cooperation is a milestone of sorts -- that the last remaining defendant who was helping former special counsel Robert Mueller and related prosecutions has wrapped.

(Former national security adviser Michael Flynn also has not yet been sentenced, but prosecutors are no longer using him as a cooperator.)

On the stand

Gates could reveal at Stone's upcoming trial some of the most tantalizing still-secret information Mueller found about the President.

According to the Mueller Report, Gates told the special counsel what Trump himself had said during the 2016 campaign related to WikiLeaks and Russian hacking.

"Gates recalled Trump being generally frustrated that the Clinton emails had not been found," Mueller wrote in a heavily redacted section of the report about the Trump campaign and WikiLeaks' dissemination of Democratic emails that had been hacked by the Russians.

Gates' efforts appeared to include Trump directly.

"According to Gates, by the late summer of 2016, the Trump campaign was planning a press strategy, a communications campaign, and messaging based on the possible release of Clinton emails by WikiLeaks," the Mueller report says.

The Justice Department then redacted two lines of the Mueller report, except for the words "while Trump and Gates were driving to LaGuardia Airport."

There's another redaction of half a line of text, before Mueller writes: "Shortly after the call candidate Trump told Gates that more releases of damaging information would be coming."

Stone has pleaded not guilty to charges of lying, obstruction and witness tampering related his efforts to reach WikiLeaks during 2016.

A star witness

Gates was a top official on both the Trump campaign and during the inauguration, and became perhaps Mueller's most important cooperator as the special counsel's office looked into Russian influence in Trump's operation. He'll likely be a star witness at all trials where he will testify.

Gates already was a key witness in Manafort's federal criminal trial for financial crimes last summer, telling the story of how his former boss orchestrated a payments system to hide their Ukrainian lobbying income from US authorities for years.

"I'm here to tell the truth. ... Mr. Manafort had the same path. I'm here," Gates told the jury last July.

Manafort and Gates had been indicted at the same time before Gates flipped. Manafort was convicted at the trial and later pleaded guilty. Manafort was sentenced to a total of about seven years in prison in March. He still faces the New York state fraud case and has pleaded not guilty there.

Gates is also lined up to take the stand later this month at the federal trial of Craig, the former Obama White House counsel. Craig's case, about his alleged unregistered lobbying work for Ukraine alongside Manafort, was spun off from the Mueller investigation. Craig, who became a lawyer at a large law firm following his work in the Obama administration, has pleaded not guilty and the trial is set to start August 12.

End of cooperation

The prosecutors and defense team's joint filing Thursday on Gates asked for the court to commission a report from the probation office that all criminal defendants receive before sentencing. That report is due November 15, Judge Amy Berman Jackson said Friday. This type of report is kept private and is used by judges as a sentencing guide.

The deadline makes it possible for him to be sentenced in the weeks after that. No sentencing date has been set yet.

"Because the defendant has been cooperating for an extended period of time, and because of the defendant's personal matters ... the defendant wishes to be sentenced as soon as possible after the completion of his cooperation with the United States," the filing said.

The filing did not describe the "personal matters" publicly, though the judge is aware of them through sealed information given to the court, the filing said.

Though initially charged with dozens of financial crimes alongside Manafort in October 2017, Gates pleaded guilty to two counts in Mueller's investigation, conspiracy and making a false statement to investigators.

At first following his indictment Gates was under house arrest, grew a beard and made appeals to the public for financial help with his legal defense. But following his plea, Gates' whereabouts went under the radar, as he stood by his pledge to help investigators and gained more ability to travel while awaiting sentencing.

A judge placed a gag order on him and his lawyers early in their proceedings, so Gates' public statements about what he was doing for Mueller and other investigators have been scarce.

Gates' stunning reversal to help Mueller in February 2018 led to intense speculation about his usefulness in building a bigger case in the Russian conspiracy investigation or against other parts of the Trump operation.

In a previous update to the court, Gates' team said his visits with federal investigators for cooperation interviews were "numerous."