Trump pardoned Cheney's former chief of staff, who was convicted in 2007 on obstruction of justice and perjury charges related to the investigation into the leak of former Central Intelligence Agency agent Valerie Plame's identity.
President George W. Bush had commuted the sentence but would not grant a pardon.
The prosecutor in Libby's case was Patrick Fitzgerald, a long-time friend of former FBI Director James Comey. He served as FBI Director from 2013-2017 when he was sacked by Trump. "I don't know Mr. Libby, but for years I have heard that he has been treated unfairly", the president said in a statement.
In a statement explaining Trump's action, the White House noted that in 2015, one of the key witnesses against Libby had recanted her testimony, among other factors.
The fact that Bush never offered Libby a full pardon created friction between the former president and his vice president. Three years later, he was cleared to practice law again after the District of Columbia Court of Appeals reinstated him to the D.C. Bar. Trump has been attacking the FBI amid the investigation of his 2016 presidential campaign for possible links to Russian meddling in the 2016 election.
"Suffice to say, he's thrilled", she said of Libby, who she said had just gotten out of an MRI.
Before Libby's pardon, today, Plame questioned Mr. Trump's motivations. Paul Krugman denounced his "deadly narcissism" in the New York Times, by which he means that Trump values his own opinion more than that of Krugman.
Plame, appearing on MSNBC on Friday before the pardon was issued, said granting one would send a message "that you can commit crimes against national security and you will be pardoned".
Libby's attorneys, Joseph diGenova and Victoria Toensing, issued a statement thanking Trump for "addressing a gross injustice" they said was inflicted by Fitzgerald and Comey. Last year, he pardoned Joe Arpaio, a former Arizona sheriff who campaigned for Trump, less than a month after he was convicted of criminal contempt in a case involving racial profiling.
Mr. Manafort was indicted in October for hiding that he was working for a Russian-backed Ukrainian party while lobbying in the United States; charges against him could put him away for the rest of his life. His record since his conviction is similarly unblemished, and he continues to be held in high regard by his colleagues and peers.
Finally, neither Mr. Trump nor his thoroughly outmatched legal team knows the full exposure he or potential witnesses face.
If Ms. Miller had testified accurately, she would have dealt a severe blow to Mr. Fitzgerald's central contention that Mr. Libby was lying when he said he was surprised to hear Russert mention Ms. Plame.
NPR political reporter Jessica Taylor contributed.