Maher, 36, was a founder and spokesman of the April 6 protest movement that was influential in the uprising that overthrew longtime ruler Hosni Mubarak.
A security source told AFP that Maher was released from jail Wednesday evening while his lawyer, Anas Sayed, said he will be under judicial supervision for three years.
Maher was arrested in November 2013 while protesting in Cairo against a law banning public gatherings not pre-authorized by the interior ministry.
He was convicted alongside prominent activists Mohamed Adel and Ahmed Douma, who as of Thursday were still incarcerated.
Rights groups say President Abdel Fattah al-Sisi's government has tried to repress all opposition since the former army chief overthrew his predecessor Mohamed Morsi in 2013.