An American pastor who had been imprisoned in China for nearly 20 years was released unexpectedly on Sunday and has returned to the United States, according to the State Department.

The pastor, David Lin, 68, was detained in 2006 and later sentenced to life in prison for contract fraud. He had been trying to open a Christian training center in Beijing; his supporters said the Chinese authorities often brought fraud charges against leaders of “house churches” and other religious establishments not controlled by the ruling Communist Party.

Mr. Lin was one of three Americans who the State Department had labeled “wrongfully detained” by China. Generally speaking, that is a designation Washington uses for U.S. citizens who it says were taken hostage to influence American policy. Dui Hua, a U.S.-based human rights group, estimates that more than 200 other Americans are “under coercive measures” in China.

Mr. Lin’s daughter, Alice Lin, told Politico in an interview that “no words can express the joy we have” about his release.

“We have a lot of time to make up for,” she was quoted as saying.

The United States had repeatedly pressed Beijing to free Mr. Lin, including last month during a visit to China by Jake Sullivan, the White House national security adviser. Since Mr. Lin’s sentencing, the Chinese government had reduced his sentence three times; he had been scheduled for release in 2029 when he was freed.

The Chinese government has made no public statements about the release. But it has made efforts to stabilize relations with the United States in recent months as China’s economy has struggled. Despite flare-ups over trade restrictions, Taiwan and other issues, Chinese officials have agreed to more military-to-military communications with their American counterparts, and they have taken steps to restrict the flow of fentanyl into the United States.