Maher, 36, was a founder and spokesman of the April 6 protest movement, one of the main groups that campaigned for more freedom under longtime ruler Hosni Mubarak.
A security source told AFP that Maher was released from jail on Wednesday evening.
But he must still spend every night at a police station, from six in the evening until six in the morning, for three years, his lawyer Anas Sayed told AFP.
His release was welcomed by Nobel peace prize winner Mohamed ElBaradei, a former UN atomic agency chief.
"You and your colleagues were at the forefront of those defending rights and supporting the oppressed," ElBaradei, a key Egyptian oppositionfigure, wrote on Twitter.
Founded in 2008 with calls for democratic change and social justice through methods including social disobedience, April 6 later became one of the influential groups in the uprising that overthrew Mubarak.
Its co-founder Mohamed Adel and activist Ahmed Douma were handed three-year sentences along with Maher in December 2013 after they were accused of organising an unauthorised protest.
All three defendants were leading dissidents under Mubarak and rose to prominence during and after the uprising.
As of Thursday, Adel and Douma were still incarcerated.
In April 2014, an Egyptian court banned the April 6 youth movement, whose coordinator Amr Ali is serving a two-year prison sentence.
Maher and Douma were arrested after Maher's supporters allegedly scuffled with police outside a Cairo court in November 2013, whenMaher handed himself in for questioning on suspicion he had organised an illegal protest.
Days earlier, the government issued a law banning public gatherings not pre-authorised by the interior ministry.
The law was issued amid a crackdown on the Muslim Brotherhood movement after then army-chief Abdel Fattah al-Sisi led the military ouster of Islamist president Mohamed Morsi in July 2013.
Morsi's Muslim Brotherhood was blacklisted after the overthrow of the Islamist, who was Egypt's first freely elected leader.
Sisi was elected president the following year. Rights groups accuse the authorities of trying to repress all opposition in a crackdown whose targets included secular activists.
