A federal court has moved to dismiss charges against ex-National Security Adviser Michael Flynn, one of several Trump associates convicted of lying.
Flynn, a former three-star US general, was the highest ranking official snared by the special counsel inquiry into Russian meddling in the 2016 election.
The ruling came as a prosecutor told Congress he was pressured to go easy on long-time Trump aide Roger Stone.
Stone has been sentenced to 40 months in jail for election-related crimes.
The surprise 2-1 ruling by the US Circuit Court of Appeals for the District of Columbia came after Flynn pleaded guilty to lying to FBI investigators about his conversations with the Russian ambassador to Washington.
It follows a highly criticised request from the Department of Justice (DOJ) to drop the case and an attempt by Flynn to change his guilty plea.
The ruling orders the judge overseeing the Flynn case to immediately drop all charges and cease his evaluation of the DOJ decision to drop the long-running prosecution. If the case is not appealed, Flynn will be legally exonerated.
President Trump cheered the “great” ruling in a tweet and called for fired FBI director James Comey to apologise to him.
The case of Flynn, who first came to many Americans’ attention with his chants of “lock her up” at Trump campaign rallies in 2016, has become a political lightning rod. Mr Trump has argued that his prosecution – as well as several other of his close associates – was motivated by his political enemies in the DOJ.
He left the White House 24 days into the job after acknowledging that he had misled Vice-President Mike Pence about his conversations with the Russian ambassador.