The 43-year-old activist and journalist had spent almost two years in detention after being arrested in October 2019.
She had been charged with “spreading false news” and collaborating with a terrorist group.
Her lawyer confirmed on Sunday that Abdel Fattah was out of prison, hours after the surprise decision to release her.
Esraa Abdel Fattah has a long history of activism and played a prominent role in the 2011 protests which helped topple the decades-long rule of the regime of Hosni Mubarak.
She was one of the first Egyptian activists to use social media to help organise anti-government demonstrations, earning her the nickname “Facebook Girl”. She was later nominated for the Nobel Peace Prize and named a Woman of the Year by Glamour magazine.
Abdel Fattah had been in pre-trial detention since being taken into custody amid a wave of arrests back in 2019.
Egypt’s current leader, President Abdul Fattah al-Sisi, has overseen what human rights groups say is an unprecedented crackdown on dissent.
He has been in power since leading a military coup in 2013 that ousted Egypt’s first democratically elected president.
Abdel Fattah claimed she had been tortured by security forces while in custody and went on a hunger strike in protest.
Her arrest and alleged treatment attracted international condemnation.
A number of other prominent journalists and opposition figures, including activist Gamal El-Gammal and Abdel Nasser Ismail – leader of the Popular Alliance party – were also freed this weekend.
However the releases come days after US officials voiced fresh concerns after another prominent activist was indicted in Egypt.