According to Christian Solidarity Worldwide, Sudanese security officials arrested Pastor Kwa Shamal, of the Sudan Church of Christ, at his home in December after he unsuccessfully campaigned against the demolition of his church in Khartoum in 2014.
Sudanese authorities only gave a day's notice before razing his church to the ground.
Two other Christians were also released in December - Revd Hassan Abduraheem and activist Talahon Nigosi Kassa Ratta - who are still being held without charge and in an unknown location.
Revd Abduraheem is a colleage of Revd Shamal's in the Sudan Church of Christ, while Talahon Ratta is a member of the Sudan Evangelical Presbyterian Church.
Both have been campaigning against the government confiscation of their church's property.
CSW's Chief Executive Mervyn Thomas said: "Whilst welcoming the unconditional release of Reverend Kwa Shamal, we remain concerned by the continuing incarceration of Reverend Hassan Abduraheem and Talahon Nigosi Kassa Ratta.
"The arrest and detention of these men are arbitrary and violate their right to liberty and security of person, as articulated in article 9 of the International Covenant on Civil and Political Rights (ICCPR) and article 6 of the African Charter on Human and People's Rights (ACHPR), to which Sudan is a party.
"We call for their immediate and unconditional release and appeal to the international community, in particular the African Union to hold Sudan to its international obligations."
