Robert Mueller has submitted a report on his long-awaited two year Trump-Russia investigation to the US Attorney General.
The Justice Department said Mr Mueller delivered his final report on Friday to Attorney General William Barr, who is reviewing it.
The attorney general will now have to decide how much of the report to make public.
It is not yet known if Mr Mueller found criminal conduct by Trump or his campaign, beyond the charges already brought against several aides.
Mr Mueller, a former FBI director, had been examining since 2017 whether Trump's campaign conspired with Moscow to try to influence the election and whether the Republican president later unlawfully tried to obstruct his investigation.
Trump has denied collusion and obstruction. Russia has denied election interference.
In a letter to lawmakers, Mr Barr said Mr Mueller had concluded the probe, that he is reviewing the report and will be consulting the deputy attorney general and Mueller to determine what information from it can be released to Congress.
Mr Barr told lawmakers he may be able to provide information to Congress on the report's findings as soon as this weekend, but offered no details of Mr Mueller's findings.
White House spokeswoman Sarah Sanders said: "The next steps are up to Attorney General Barr, and we look forward to the process taking its course. The White House has not received or been briefed on the Special Counsel's report.”
Mr Trump previously called the investigation a “witch hunt” and accused Mr Mueller of conflicts of interest.
The investigation has already ensnared key figures including Trump’s former campaign chairman Paul Manafort, former personal lawyer Michael Cohen and national security adviser Michael Flynn, who have either been convicted of or pleaded guilty to charges brought by Mr Mueller.
Mueller has brought charges against 34 people, including Russian intelligence officers, and three Russian companies, including one described as a "troll farm."
The inquiry was set up to answer the following questions:
- Did Mr Trump's campaign collude with the Kremlin to sway the 2016 presidential election in favour of the celebrity businessman?
- Did Mr Trump take steps later, including by firing his FBI director, to obstruct the probe?
Congressional Democrats, who took over control of the US House of Representatives in January, have said they plan to push for a release of the full Mueller report and said they would subpoena it if necessary.