White House Chief of Staff Mark Meadows (L) disembarks from Air Force One with U.S. President Donald Trump at Miami International Airport on July 10, 2020 in Miami, Florida.
Meadows reportedly told special counsel Jack Smith he repeatedly warned Trump after the 2020 election that claims of election fraud were 'baseless'.
He told prosecutors the ex-president was being 'dishonest' with the public when he said the election was stolen, ABC News reported.
The immunity deal means he could testify under oath against his old boss.
'Obviously we didn't win,' Meadows told investigators, according to the report.
Meadows served as the final chief of staff for Trump at the White House.
A lawyer for Meadows did not immediately respond to a request for comment.
In August, Smith charged Trump with four felony counts for attempting to interfere in the counting of votes and trying to block the certification of Joe Biden as the winner of the 2020 U.S. presidential election.
Trump has pleaded not guilty to the charges.
Thousands of Trump supporters stormed the U.S. Capitol on Jan. 6, 2021 in a failed bid to overturn his defeat.
Since then Trump has continued to make the false claim his loss was the result of fraud.
According to ABC News, Meadows has spoken with Smith's team at least three times this year.
That included once in front of a federal grand jury.
He did so only after being granted immunity to testify under oath, sources told ABC News.
The case is one of four criminal prosecutions Trump, 77, faces as he seeks to retake the White House.
He is the frontrunner for the Republican nomination in 2024.
Trump has previously described Meadows as a 'special friend' and 'great chief of staff, as good as it gets.'
Prosecutors were reported to have asked him about his conversations with Trump in the final months of the presidency leading up to Jan 6.
Meadows reportedly told prosecutors Trump was being 'dishonest' when, hours after polls closed on election night, he claimed to have won.
He reportedly told prosecutors he had never seen evidence of fraud that would have altered Biden's victory.
In mid-December, six weeks after the election, he told Trump such evidence had not materialized, ABC News reported.
Prosecutors reportedly asked Meadows if Trump had ever admitted to him that he believed he lost the election.
Meadows reportedly told them that he had never heard Trump say that.
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