A prominent activist in the 2011 Egyptian uprising has been released from prison after serving a three-year sentence, his lawyer said.

Ahmed Maher, a symbol of the revolution that toppled former President Hosni Mubarak, was released on Thursday.

His wife, Reham Ibrahim, welcomed his release in a Facebook post, saying: "We will make up for what we missed," expressing disbelief over her husband's return home.

Maher was charged in 2013 for attending a protest in defiance of a law banning public gatherings not pre-authorised by the Interior Ministry.

He will continue the remainder of his sentence, which is expected to last for another three years, under surveillance in his Cairo home.

One of Maher's lawyers, Mohamed Gaheen, said: "The purpose of the probation period is to watch criminals after they finish their prison terms, but it has never been used before against political prisoners."

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Maher, 36, used his activism via social media as a cofounder of the April 6 youth movement to rally Egyptian youth in the demonstrations that resulted in Mubarak stepping down in February 2011.

With the military takeover that followed two and half years later, which overthrew the elected Islamist president, the new government issued a ban on all unauthorised demonstrations.

The law on protests says the Interior Ministry must be notified of any public gathering of more than 10 people at least three days in advance.

The law allowed security forces to step up force and to issue verbal warnings to protesters, use water cannon or tear gas and birdshot against demonstrators.

The current government under President Abdel Fattah el-Sisi has waged a large-scale crackdown on opposition over the past few years, including Islamist supporters of former President Mohamed Morsi, and other secular activists.

It is uncertain whether Maher will be able to return to activism given the current political climate.

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Maher was convicted along with prominent activists and cofounders of the movement Mohammed Adel and Ahmed Douma. Each was fined and sentenced to three years in prison. While Adel will end his sentence in one month, Douma is serving a life sentence in another case and is awaiting an appeal in April.

Founded in 2008 with calls for democratic change and social justice through methods including civil disobedience, the April 6 movement later became one of the influential groups in the uprising that overthrew former President Morsi.

Tarek al-Awadi, a lawyer also serving in Maher's case, said that local police assigned with monitoring him, would have wide discretion over his treatment.

"If they decide to put a lot of pressure on him, humiliate him and treat him like they treat thieves and drug dealers, they could order him to spend each night of the coming three years at the police station," al-Awadi said.