Mraz has a history of involvement with human rights and other social causes.
But there was some criticism of his visit by campaigners for Myanmar's Muslim Rohingya community, which has been the target of ethnic-based violence this year that has forced tens of thousands of people from their homes into makeshift refugee camps. They feel Myanmar's government has been complicit in the discrimination, and that Mraz's visit provides it cover with the image of being a defender of human rights.
Mraz said he was aware of the issue, but that if he didn't come to do the concert because someone else had asked him to protest another problem, then that would not help tackle the exploitation and human trafficking issue.
"I understand that there is a lot of wrongdoing in this world," he said. "Today I'm here for this."
Walk Free used the occasion of Sunday's concert to launch a campaign calling on the world's major corporations "to work together to end modern slavery by identifying, eradicating and preventing forced labor in their operations and supply chains." They are seeking to have the companies make a "zero tolerance for slavery pledge" by the end of March next year.
"While many think of slavery as a relic of history, experts estimate that there are currently 20.9 million people living under threat of violence, abuse and harsh penalties," the Australia-based group said in a statement. "Within this massive number, the majority of people - more than 14.2 million - are in a forced labor situation, used to source raw materials, and create products in sectors such as agriculture, construction, manufacturing and domestic work."