Wong, 21, who became the face of the mass pro-democracy protests while still a teenager, was imprisoned for six months while Law...
A defiant Wong said the activists stood ready to face what he called "suppression by an authoritarian regime" as he stood alongside Law outside the Court of Final Appeal following the decision.
"The government can lock up our bodies but they can't lock up our minds," he told reporters.
"They cannot put aside our determination to fight for democracy."
The pair were jailed in August after the Beijing-backed Hong Kong government pushed for tough sentences. Fears are growing that China is tightening its grip over the semi-autonomous city and that the rule of law is being compromised.
Wong, 21, who became the face of the mass pro-democracy protests while still a teenager, was imprisoned for six months while Law, 24, was sentenced to eight months.
They were granted bail Tuesday until November 7, the first appearance in appeal proceedings against the jail terms.
A third activist, Alex Chow, who was jailed for seven months alongside Law and Wong, was not part of the hearing.
Emerging from the courthouse in a neat white shirt and with his hair growing back after being shaved in prison, Wong said he planned to enjoy a meal with his family Tuesday night.
Law told reporters there had been "unpleasant times" behind bars.
"I hope the result of the case showcases the protection of human rights in our law system," Law said of the activists' appeal.
"The world is watching."
Hong Kong enjoys freedoms unseen on the mainland under a "one country, two systems" deal made when Britain handed the city back to China in 1997.
But Beijing stands accused of breaching the agreement.
Supporters outside punched the air at news of the pair's release.
Lawmaker Eddie Chu said it was "encouraging news for supporters of democracy".
The Umbrella trio were found guilty last year on unlawful assembly charges for storming a fenced-off government forecourt known as "Civic Square" as part of a September 2014 protest calling for fully free leadership elections.
Their arrests sparked wider rallies which exploded two days later when police fired tear gas at the crowds. This triggered demonstrations that blocked some major roads for more than two months in an unprecedented challenge to Beijing.
Wong and Law initially received community sentences and Chow a three-week suspended sentence at a magistrates' court over the Civic Square protest.
But Hong Kong's justice department applied to increase those terms, with prosecutors arguing they should receive harsher punishment.
The judgement jailing them in August said the court must "send out a clear message to society" that protesters must abide by the law.
Wong's imprisonment prevented him from running for Hong Kong's partially directly elected legislature.
Law had already succeeded in becoming a legislator but was among six rebel lawmakers disqualified from parliament after inserting protests into their oaths of office.
Wong and Law each offered cash bail of HK$50,000 ($6,400). They were required to surrender their passports and to report to police once a week.
Wong has yet to be sentenced on a separate charge of contempt for obstructing the clearance of a major encampment during the Umbrella Movement rallies.
He has pleaded guilty to that charge.