Prominent Beijing-based lawyer Zhang Kai was seized after defending churches in the courts against moves to tear down their crosses.
He was arrested on August 25 2015 ahead of a meeting with the US ambassador at-large for religious freedom.
The lawyer was accused of 'endangering national security' and 'gathering crowds to disturb the social order' - charges he has now been made to confess to on TV.
Zhejiang, a significantly Christian area in China has had thousands of crosses removed from buildings over the last two years.
There is now concern that no Christian crosses could be left standing on churches in the province after Easter.
Christian charity, Release International, which supports persecuted Christians, has said that it is concerned the campaign of intolerance towards Christians in Zhejiang could spread to other parts of China.
It has been reported that another 49 crosses have been taken down since the start of year.
Release International says if churches do not take them down themselves the authorities are stopping amenities to the buildings like electricity and water.
So far around 1850 crosses have been removed.
Release International chief executive Paul Robinson said: "Our partners report growing fears that no Christian crosses could be left standing there after Easter.
"And there are concerns this campaign to curtail the visible Christian presence in the province could gather momentum and spread across China."
The petition calling for Zhang's release was launched days before a televised confession, which some have accused of being forced, in which the leading lawyer, apparently reading from a script, admits to endangering national security and confess his 'deep remorse'.
The petition also calls on the President to release hundreds of Chinese lawyers who have been harassed, held illegally and denied legal representation.
Paul Robinson continued: "There's a terrible irony here."
"China is rounding up its human rights lawyers for attempting to uphold the rule of law and is denying them legal rights.
"What message does this mockery of justice give to the rest of the world? Why is this emerging superpower so insecure that it has to resort to silencing its lawyers? Pray for Zhang Kai. Stand with him."