Private Manning later said that she is uncertain where her life will take her after serving seven years in jail.
She said in a statement that "whatever is ahead ... is far more important than the past", and that she is "figuring things out right now".
The statement was emailed just hours after her release from a military prison in Kansas.
Minutes later, she tweeted a photo of her feet in tennis shoes, with the caption: "First steps of freedom!!"
Chelsea Manning has been released from a Kansas military prison after serving seven years of her 35-year sentence for leaking classified government materials to WikiLeaks.
US army spokeswoman Cynthia Smith said Private Manning was released from Fort Leavenworth on Wednesday.
Former president Barack Obama granted Manning clemency during his final days in office.
Manning, an Oklahoma native, was convicted in 2013 of 20 counts, including six Espionage Act violations, theft and computer fraud.
She was acquitted of the most serious charge of aiding the enemy.
The former intelligence analyst in Iraq acknowledged leaking the materials, saying she wanted to expose what she considered to be the US military's disregard of the effects of war on civilians.
She was known as Bradley Manning before transitioning in prison.