For a time, Christians who converted in order to divorce were allowed by the courts to formally return to their original faith. But in recent years, as a more conservative sentiment has spread throughout the country and the government, the courts have not allowed converts to return to Christianity.

“Our request was fully granted,” said Hossam Bahgat, director of the Egyptian Initiative for Personal Rights, a group based in Cairo that filed the case in association with Human Rights Watch. “The defendants are going to receive their ID cards, as Christians.”

Egyptian law does not officially prevent Muslims — whether they are former Christians or not — from leaving their religion. While it is relatively easy to convert from any faith to Islam, government officials have taken the view that leaving Islam is apostasy, and therefore is not permitted.

With its decision, the court has reversed a lower court ruling forbidding reconversion. But it also appears that the court has not opened the door for lifelong Muslims to convert to Christianity. Last month, the same court ruled against allowing Mohammed Ahmed Hegazy, a Muslim convert to Christianity, to have access to official papers conforming to his new religion.

“It’s a big step for religious freedom in Egypt, but religious freedom will only be fully reached once Muslims can convert to Christianity,” said Ramsis el-Naggar, a lawyer who worked on behalf of the 12 converts.

The ruling comes in the context of a wider legal battle over identity cards and minority rights in the country.

On Jan. 29, another ruling by the Court of Administrative Justice prohibited the Egyptian government from withholding official documents to Baha’is. Baha’is, a small religious minority in Egypt, were forced to register as Christians, Muslims or Jews, the only three options approved by the government. Those who refused to accept any of those three were penalized: they could not register their children in school or open a bank account, for example.

“The important story is that there has never been so much discussion on issues of conversion, apostasy and not only among intellectuals,” Mr. Bahgat said. “It is starting to go to the courts now.”