Yaser Tabbara may live half a world away from Syria, where he grew up. But as the uprising there continues, the Chicago lawyer has mounted a one-man legal and diplomatic assault against the Syrian regime to highlight the brutality of its response and help depose President Bashar al-Assad.

In recent weeks, Mr. Tabbara, 35, attended opposition conferences in Turkey and Belgium, and spoke at policy forums in Qatar and Washington. He also built a case for the prosecutor of the International Criminal Court to charge the Syrian government with crimes against humanity, and he helped draft a letter to the United Nations Security Council calling for urgent action — all while communicating with protesters inside Syria and occasionally representing his law firm’s clients in Chicago courts.

Few people would seem better qualified to lend external support to the uprising. A human rights lawyer born in Chicago and raised in Damascus, Mr. Tabbara has a long history of activism and is practiced in Western justice as well as in the ways of international courts and Syrian politics.

Since mid-March, Mr. Assad has turned his security and military forces loose on the protesters; activists say some 1,400 Syrians have been killed. Watching from afar, Mr. Tabbara said he had been motivated by “a very objective sense of outrage and a sense of responsibility that this country cannot be led by this Mafia-esque gang.”