Manning came out as a transgender woman in prison.
As a prisoner at the US Disciplinary Barracks at Fort Leavenworth in Kansas, she had to conform to male grooming standards before her 3 a.m. ET release.
"She has experienced trauma over the past seven years of her confinement and the trauma from those experiences won't just evaporate the day she walks out of prison," said American Civil Liberties Union lawyer Chase Strangio, who represented Manning.
"It's going be a process for her to heal and begin to live her free life with more autonomy over her gender and her decisions and vision for the future."
After her release, Manning said in a statement, "After another anxious four months of waiting, the day has finally arrived. I am looking forward to so much! Whatever is ahead of me is far more important than the past. I'm figuring things out right now -- which is exciting, awkward, fun, and all new for me."
She also tweeted a photo of her feet, clad in black, low-top Converse Chuck Taylors, with the caption, "First steps of freedom!!"
The Army says Manning will remain on unpaid, active-duty status as she continues to appeal her court-martial. This means she will maintain her access to military medical benefits, including for gender dysphoria and gender reassignment, but Strangio said his client has no interest because of the treatment she endured in prison.
"Because of the nature of her circumstances and the experience of confinement, she is very committed to living her life as free from the government as possible and taking care of her own health benefits and financial needs, separate and apart from the continued benefits available to her," the lawyer said.
Manning was convicted in 2013 of stealing 750,000 pages of documents and videos before leaking them to WikiLeaks
Manning -- known then as Bradley Manning -- was sentenced to 35 years in prison on 20 counts
, including violations of the Espionage Act.
After the 2013 sentencing, the ex-intelligence agent changed her name to Chelsea Manning
and identified as transgender.
As one of his final acts in office, President Barack Obama commuted Manning's sentence
in January, giving her an early release date.
Last week, Manning tweeted her excitement about her impending release
: "Freedom was only a dream, and hard to imagine. Now it's here! You kept me alive. ..."
She clearly looked forward to what life might hold for her outside the military prison walls.
"For the first time, I can see a future for myself as Chelsea. I can imagine surviving and living as the person who I am and can finally be in the outside world," she said in a written statement
. "I hope to take the lessons that I have learned, the love that I have been given, and the hope that I have to work toward making life better for others."
Amnesty International, which had campaigned for Manning's release, was quick to applaud her freedom but said the fight was not over.
"While we celebrate her freedom, we will continue to call for an independent investigation into the potential human rights violations she exposed, and for protections to be put in place to ensure whistleblowers like Chelsea are never again subjected to such appalling treatment," a statement said.
Manning was one of the first service members to access transgender health care benefits under new policy and the first to be approved for gender reassignment surgery in military prison. The military also allowed her to begin taking hormones
But it didn't come easily. Manning launched a hunger strike in September, demanding access to treatment for her gender dysphoria.
She remained housed at Fort Leavenworth, an all-male Army prison, despite her request to transfer to a civilian women's prison. She had to cut her hair, exacerbating her gender dysphoria, Strangio said. She felt her situation was so dire that in July she tried to commit suicide
Though she still needs to navigate the legal process, Manning's "priority is living her life in the civilian world and taking care of her own needs."
She hopes to reside in the Washington area, the attorney said, explaining her supporters there will be vital, not only to her transition to civilian life but also to her transition to living openly as a transgender woman.
"It's going to be Chelsea telling us what her future will look like," Strangio said.
She hopes to continue hormone therapy and may pursue gender reassignment if doctors continue to recommend it, Strangio said.
Otherwise, she looks forward to growing out her hair and discovering "what will make her feel like she can embody womanhood" without the government's interference, he said.
Obama's decision to commute Manning's sentence set off harsh criticism from some Republicans
and intelligence officials. But Obama said she had served a "tough sentence."
Manning's attorneys Nancy Hollander and Vincent Ward agreed.
"Chelsea has already served the longest sentence of any whistleblower in the history of this country. It has been far too long, too severe, too draconian," Hollander and Ward said in a joint statement.
"President Obama's act of commutation was the first time the military took care of this soldier who risked so much to disclose information that served the public interest."