“The cross-border repression of which Teng Biao himself has become a victim has become this whole new complex set of issues,” said Eva Pils, a scholar at King’s College London, who once directed a center at the Chinese University of Hong Kong that hosted Mr. Teng. “I’m wary of how repression crosses borders, and I’m wary of how China is changing norms.”

Mr. Teng and his family also ran into financial difficulties in the United States after his wife was dismissed from her job as an international representative for a Chinese technology parts company — a move that he said had been forced by Chinese officials. His wife had worked for the company for 17 years.

“The Chinese government put pressure on that company,” Mr. Teng said. “The company said that because of me, they couldn’t sell their products to Chinese agencies and the military.”

Mr. Teng grew up in a village in the northeastern province of Jilin. His father was a painter and held a low-level official post related to education and culture, while his mother worked as a farmer. He received a slot at prestigious Peking University and decided to study law, eventually earning a doctorate in law in 2002.

While teaching at the China University of Political Science and Law, he became involved in the case of Sun Zhigang, a migrant worker killed by the police while in detention in the south. This started Mr. Teng and other lawyers on the road to activism, leading to their harassment by officials.

Mr. Teng and his wife watched with growing anxiety as President Xi Jinping tightened control over civil society after taking power in 2012. Mr. Teng already had been detained repeatedly and beaten by police officers, with his family illegally kept in the dark as to his whereabouts for weeks at a stretch.

He went to the Chinese University of Hong Kong as a visiting scholar in 2012, then flew to the United States with his younger daughter two years later after getting an invitation from Harvard. By then, his wife and elder daughter had been barred from leaving the mainland, but they fled through Southeast Asia in 2015 with the help of smugglers, at one point riding on the backs of motorbikes through the hills of Thailand.