The 29-year-old, who underwent a gender transition in prison, has taken to Twitter to celebrate, saying "First Steps of Freedom, #ChelseaISFree".
The New York Times reports that Manning was "sentenced to an unprecedented 35-year prison term for disclosing archives of secret files to WikiLeaks", some of which the newspaper published, but was not criminally charged for doing so.
Manning twice attempted suicide past year at Fort Leavenworth, a male military prison.
Her sentence was commuted in President Obama's final months in office, a controversial move which was cheered by advocates and pro-whistleblower groups.
The military was therefore keen on keeping her release low-key.
While Manning's sentence was commuted, her conviction remains intact.
The Oklahoma native was convicted of 20 counts including theft, computer fraud and six violations of act. Manning launched a hunger strike in September, demanding access to treatment for her gender dysphoria.
Check out Manning's celebratory post, below.
She had passed 700,000 pages of revelatory material about United States military operations in Iraq and Afghanistan to WikiLeaks, which included videos of the Baghdad airstrike on 12 July 2007 and the 2009 Granai airstrike in Afghanistan.
"Pvt. Manning is statutorily entitled to medical care while on excess leave in an active duty status, pending final appellate review", said Army spokesman Dave Foster. She served seven years out of 35 and on Wednesday, she finally walked free. "I can imagine surviving and living as the person who I am and can finally be in the outside world". "Chelsea Manning's treachery put American lives at riskand exposed some of our nation's most sensitive secrets", Ryan responded to the news of Manning's sentence commutation.
She wasn't able to flee overseas like Edward Snowden, who in 2013 released documents showing that the NSA was sweeping up USA citizens' communications metadata.
Speaking to the BBC, Manning's friend, the journalist Glenn Greenwald - who was involved in the publication of leaks from Edward Snowden - said she faced a hard life outside prison.
Chelsea Manning was released from prison Wednesday.
Critics of Manning's decision said that she had released information identifying military informants, potentially putting them at risk. But Obama said she had served a "tough sentence".