The decision has been made a week after Kim Kardashian West pleaded her case in a meeting with Trump at Oval Office.
As for how she received news of her release, Johnson said Kardashian was the one who told her she'd get to go home.
Sal Rodriguez is an editorial writer and columnist for the Southern California News Group.
Trump has also pardoned conservative author and filmmaker Dinesh D'Souza, Arizona sheriff Joe Arpaio, former Vice President Dick Cheney's chief of staff I. Lewis "Scooter" Libby and Kristian Saucier, a Navy sailor.
"To have the President of The United States feel that I deserve a second chance makes me feel so grateful to him".More news: Citing injury, Serena Williams pulls out of French Open
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Kardashian West joined what has been a long-running campaign for Johnson's freedom, spearheaded by the clemency foundation CAN-DO, friends and family.
The Washington Post reports that senior White House aides believe that Trump has become "fixated on his ability to issue pardons", which they describe as his "new favourite thing".
Do you think more celebrities should involve themselves in politics? And he granted a posthumous pardon to boxing's first black heavyweight champion, which had been championed by actor Sylvester Stallone.
Johnson was convicted and sentenced to life in prison for her involvement facilitating communications within a 1996 cocaine trafficking operation. "Telling her for the first time and hearing her screams while crying together is a moment I will never forget". Though Johnson had had no criminal record, she was sentenced to life in prison with no parole.
Trump has commuted Ms. Johnson's sentence.
"I want to tell my war angel, thank you for never giving up, you did it, you fought and you fought until I was free", she said.