"She is no longer qualified to be Hong Kong's leader," Wong told reporters. "She must take the blame and resign, be held accountable and step down."
Wong was sent to prison in May after he lost an attempt to quash a jail sentence over the huge democracy protests he helped lead in 2014.
His release comes as Hong Kong is rocked by historic anti-government protests. They were initially sparked by mass public opposition to a plan to allow extraditions to China.
But the movement has since morphed into the latest expression of public rage against both the city's leaders and Beijing.
Speaking to the media outside Lai Chi Kok Correctional Institute, 22-year-old Wong called on protesters to continue their protests and civil disobedience campaign.
"We demand Carrie Lam to step down, completely withdraw the extradition law, and retract the 'riot' label," he said, referring to Lam's previous term to describe protesters earlier in the week.
He also condemned authorities for firing tear gas and rubber bullets during violent clashes between protesters and police on Wednesday.
"When I was in jail, I saw Carrie Lam crying on the live television broadcast. All I can say is, when she shed tears, Hong Kong citizens were shedding blood in Admiralty," he said, referring to the district where the clashes took place.