Most of what remained of her 35-year sentence was commuted by then-US President Barack Obama in January.
Little information has been released about the details of her departure from Fort Leavenworth military prison in Kansas.
Her lawyer said she was excited but likely "anxious".
A day after she was sentenced to 35 years in prison in 2013 Manning said she had felt female since childhood and wanted to live as a woman called Chelsea.
"For the first time, I can see a future for myself as Chelsea," she said in a statement last week ahead of her release. "I can imagine surviving and living as the person who I am and can finally be in the outside world."
'Back to Maryland'
Chelsea Manning was convicted of 20 charges in connection with the leaks, including espionage. She was acquitted of the most serious charge, aiding the enemy.
She defended the leaking by saying she had wanted to spark a public debate in the US about the role of the military and US foreign policy, but later apologised for "hurting the US", saying she had mistakenly believed she could "change the world for the better".
In January she tweeted that she wanted to move to Maryland after being released, a state where she previously lived.
On Monday she tweeted: "Two more days until the freedom of civilian life ^_^ Now hunting for private #healthcare like millions of Americans =P".
Chelsea Manning will remain on active army duty while her military court conviction remains under appeal. She will have healthcare benefits but will be unpaid, the army says.
If the appeal is denied, she could be dishonourably discharged from the army, US media say.
Chelsea Manning has been held in an all-male facility
Chelsea Manning was deployed to Iraq as an intelligence analyst when she leaked hundreds of thousands of files to Wikileaks.
Included in those files was video footage of an Apache helicopter killing 12 civilians in Baghdad in 2007, and many sensitive messages between US diplomats.
Barack Obama's decision to commute her sentence drew criticism from leading Republicans, including Senator John McCain, who called it a "a grave mistake".
Manning twice attempted suicide last year at Fort Leavenworth, a male military prison.
She also went on a hunger strike last year, which she ended after the military agreed to provide her with gender transition treatment.