Christian human rights campaigners have hailed Sudan's abolition of the apostasy law a "miracle".
The government of Sudan, where Christians have suffered persecution for many years, decided to relax the law in April but the changes only came into effect last week.
"The direction of travel in Sudan was towards ever-tighter Islamic law and restrictions on religious freedom. Today that direction of travel is being reversed. There is freedom in the air," said Paul Robinson, CEO of Release International, which supports persecuted Christians worldwide.
For many years, it was illegal to convert to Christianity in Sudan and even discussing religious beliefs could lead to arrest. The penalty for apostasy under the former Islamist government was death.
In 2014, Sudan's apostasy laws came under the spotlight when one woman, Meriam Ibrahim, was sentenced to death and 40 lashes for supposedly committing the crime after she married a Christian man.
Although she was Christian herself, she was charged with apostasy because her father's faith was Muslim. She was sentenced to death after refusing to renounce her Christian faith and gave birth while on death row in prison before finally being released and fleeing to Italy.
Mr Robinson said the decriminalization of apostasy in Sudan was "a significant move towards religious freedom in a country where Christians were routinely persecuted".
That persecution has also seen Christian property seized by the authorities, which he said he is now hoping will be returned.
Mr Robinson asked Christians to pray that religious freedom will be protected in Sudan against possible opposition.
"Opposition is to be expected and there is the risk of a backlash by hardliners," he said.
"Pray that freedom will win the day and that Christians will have a stronger voice under the new administration. Please pray also that the government will return the many Christian and Church-owned properties that have been seized."
The changes have been brought in by the transition government that replaced the dictatorship of Omar al-Bashir, who was toppled last year.
On Saturday, Sudan's justice minister announced that the country will now permit non-Muslims to consume alcohol, and that female genital mutilation (FGM) is to be banned.