In July, Bush commuted Libby's 2 1/2 -year sentence, sparing Vice President Cheney's former chief of staff from serving any prison time after being convicted of perjury and obstructing justice. Libby, who recently dropped appeals to have his convictions overturned, has paid a $250,000 fine and remains on two years probation.
Libby was the only person to face criminal charges in the case of the 2003 leak of then-CIA operative Valerie Plame Wilson's identity.
A pardon amounts to federal forgiveness for one's crime, while a commutation cuts short an existing prison term.
Justice Department spokesman Erik Ablin said Bush has granted 142 pardons and commuted five sentences since taking office in 2001.