Mudawi Ibrahim Adam, arrested from his home in January, was released on Wednesday, Sabah Mohamed Adam told Reuters.
"He was released yesterday and is in Faysal hospital in Khartoum," she said, adding that he was in hospital to recover from the effects of his hunger strike in detention.
It was not clear when Adam ended his hunger strike.
Asked if there were any charges brought against her husband, she said: "Only for the hunger strike. It is a crime to try to kill yourself in Sudan."
Adam had previously been arrested and charged with crimes against the state for his work promoting human rights in Sudan's troubled Darfur region, in the grip of a 25-month-old rebellion. That went to trial but all charges were eventually dropped.
Adam is the chairman of the Sudan Social Development Organisation, which has given aid and disseminated human rights information in Darfur. Almost 2 million have fled their homes in Darfur and ten of thousands have been killed in the fighting.