Wong, 21, who became the face of the mass pro-democracy protests while still a teenager, was jailed for six months while Law...
The sentences handed down by the city's Court of Appeal in August came as fears mount that Beijing is tightening its grip on 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 jailed for six months while Law, 24, was imprisoned for eight months.
They were granted bail at the Court of Final Appeal until November 7, the first appearance in the appeal proceedings.
A third activist, Alex Chow, who was jailed for seven months alongside Law and Wong, was not part of Tuesday's hearing.
On emerging from the courthouse, a sombre Law said there had been "unpleasant times" in prison and that he was looking forward to a meal with his family.
Law said the result of the appeal case would depend on "the implementation of 'one country, two systems'", the semi-autonomous deal that guarantees Hong Kong rights unseen on the mainland.
China stands accused of trampling the arrangement, made when Britain handed back Hong Kong in 1997.
"I hope the result of the case showcases the protection of human rights in our law system," Law told reporters.
Wong was still completing paperwork in the courthouse by early afternoon.
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 on the crowds, triggering demonstrations that brought parts of Hong Kong to a standstill 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 then sought 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 parliament, something he said he had wanted to do. He had been waiting to turn 21 to become eligible to stand.
He celebrated that landmark birthday in jail last month.
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) Tuesday. They were required to surrender their passports, not to leave Hong Kong and report to police once a week as part of the terms.
Wong is 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.
Other activists previously sentenced on contempt charges have received sentences of up to three months.