The 29-year-old served seven years in jail over what is believed to have been the biggest breach of classified information in US military history.
She leaked a total of 700,000 documents, diplomatic cables, videos and battlefield accounts while working as an intelligence analyst in Iraq in 2010.
Previously known as Private Bradley Manning, the soldier now chooses to identify as a woman and underwent gender transition while in jail.
Following her release, Manning posted a photo of her feet on social media alongside the caption: “First steps of freedom!!”
— Chelsea Manning (@xychelsea) May 17, 2017
Earlier, in a statement to ABC News, Manning said: “I appreciate the wonderful support that I have received from so many people across the world over these past years.
“As I rebuild my life, I remind myself not to relive the past.
“The past will always affect me and I will keep that in mind while remembering that how it played out is only my starting point, not my final destination.”
She will now assist with a documentary about her life.
Confirming Manning’s release on Wednesday, the spokesperson said: “I can confirm Manning has been released from The United States Disciplinary Barracks, Ft. Leavenworth.
“Based on privacy act restrictions there is nothing further I can provide at this time.”
Manning was sentenced to 35 years in jail in 2013 after being convicted of numerous charges, including espionage.
But, in January this year, former US president Barack Obama commuted her sentence in one of his last acts in the White House.
He described Manning’s sentence as “very disproportionate” although Mr Obama’s successor, Donald Trump, branded the soldier an “ungrateful traitor” who “should never have been released”.
Manning had been held at Fort Leavenworth in Kansas, during which time she transitioned to a woman but was denied permission to grow her hair.
She attempted suicide twice last year and also conducted a hunger strike.
Friends and family have organised a campaign to raise funds for Manning on her release, which has so far collected more than $147,000 (£114,000).
The money will pay for Manning’s living expenses for her first year out of prison.
The US Army has previously confirmed Manning will remain an active duty soldier, although in an unpaid status.