Jared Kushner, President Trump's son-in-law and senior adviser, had his security clearance restored after nearly three months in limbo.
Kushner's months-long inability to get a permanent security clearance had long vexed the administration, so much so that some officials felt unwilling to push the issue with others in similar straits.
Career officials approved the clearance following the background check, the newspaper reported.
Lowell continued to sidestep the question of whether Kushner was a target, subject, or witness, saying, "Nobody has indicated they have any intention of saying to him, you've done something wrong that would merit any charges".
Kushner's permission to view top secret information was revoked in February after White House Chief of Staff John Kelly declared a moratorium on temporary security clearances.
Kushner had been relegated to pushing Middle East diplomacy without a "Top Secret/SCI" clearance since the end of February. Mueller is investigating Russian election meddling and any ties to Trump associates.
Kushner was first interviewed in November, when the focus was mainly on former national security adviser Michael Flynn, who pleaded guilty of lying to the Federal Bureau of Investigation.
White House Chief of Staff John Kelly yanked several senior officials temporary top-level clearances in February
Lowell, in a statement, said Kushner has cooperated fully with the investigation, including sitting for two interviews with the special counsel's office.
"A year ago, Jared was one of the first to voluntarily cooperate with any investigation into the 2016 campaign and related topics", said Lowell, Kushner's lawyer.
Lowell said that Kushner answered all questions that were asked. Even without a permanent clearance, the president's son-in-law had been allowed to see materials, including the president's daily brief, that are among the most sensitive in government.
Kushner's initial SF-86 form did not mention any foreign contacts, though he quickly supplemented it to indicate that he would provide that information.
Some experts said that the evolving disclosures might have been disqualifying for another person and that it could explain the delay in granting Kushner a clearance.
Kushner - the point of contact for foreign officials during the campaign and transition - was also alluded to, though not by name, in Flynn's guilty plea as a transition team official who encouraged Flynn to contact foreign government officials, about a U.N. Security Council resolution against Israeli settlements.