The police presence was relatively light overnight.
"I will join to fight against this evil law", said Wong, one of the leaders of the 2014 pro-democracy "Umbrella" protests that blocked major roads for 79 days.
At the march's end, hundreds sat wearily around the city government headquarters.
Hong Kong still enjoys freedoms not seen on mainland China - but critics say they are on the decline.
The terms "Hong Kong", "in extradition" and "protests" are among the most-searched terms on Freeweibo.com, a site monitoring posts that have been deleted from the site.
A statement Sunday credited to an unidentified government spokesman said that unspecified "deficiencies in the government's work had led to substantial controversies and disputes in society, causing disappointment and grief among the people".
Hong Kong's pro-government camp has scrambled to try to save the image of Chief Executive Carrie Lam Cheng Yuet-ngor after the general public, rising up in Sunday's mammoth protest demonstration, criticized her for arrogance and poor governance.
Having lived in Taiwan for almost one year, Nip was dismayed to learn that some of the island's China-friendly politicians did not speak out about the protests in Hong Kong - such as Kuomintang (KMT) Kaohsiung Mayor and presidential hopeful Han Kuo-yu (韓國瑜).
The uproar over the extradition bill highlights worries that the former British colony is losing the special autonomous status China promised it when it took control in 1997.
Mexico migrant deal includes regional asylum plan - document
Trump has spent the days since Friday's announcement defending the scope of the deal. Details of the agreement will be released shortly by the State Department.
Organisers said some two million people marched in tropical heat on Sunday calling for the resignation of chief executive Carrie Lam, rebuking a now abandoned bill that would have allowed extraditions to the Chinese mainland.
The crowds, walking slowly and shouting "withdraw" and "resign", spilled into the street Sunday from downtown Victoria Park and began marching toward the Central district where the government headquarters is located.
Protesters remain unmoved by the freeing of activist Joshua Wong and the apology of the territory's chief executive Carrie Lam. Lam backed away from pushing through the legislature the measure that would enable suspects to be sent to stand trial in mainland Chinese courts.
The rally was organized by several local organizations, including Taiwan Youth Association for Democracy (TYAD), Taiwan Citizen Act Front, and a watch group established by current and former Hong Kong students studying in Taiwan, according to local media.
The government understands that protests against the legislation "have been made out of love and care for Hong Kong", a statement issued late Sunday by Hong Kong's government said.
"It's a massive repudiation of the idea that Hong Kong will be effectively, over time, fully absorbed into mainland China", said Bill Bishop, publisher of the Sinocism China Newsletter.
"It's not that different to the U.S. extraditing the Huawei executive from China", Oliver said.
Hong Kong is bracing for another massive protest over an unpopular extradition bill, a week after the crisis brought as many as 1 million into the streets.
Today's protestors in Hong Kong are demanding the cancellation of a proposed bill that would allow Beijing to extradite alleged criminals from Hong Kong, even though Hong Kong has its own legal and judicial system, unfettered internet and a free press.
Veteran opposition Democratic Party lawmaker James To said Lam had go. They also called for the police to be held accountable for their brutality on June 12.
Protesters have mainly focused their anger on Lam, who had little choice but to carry through dictates issued by Beijing, where President Xi Jinping has enforced increasingly authoritarian rule.