Ratification of the sentence comes days after she was freed over a separate case Sunday, her husband Mohamed Lotfy said. The latest ruling means Amal could be arrested at "any time" pending an appeal in Egypt's Court of Cassation, he explained.
She was detained in May days after she posted a 12-minute video expressing anger at poor service at a bank, heavy traffic, sexual harassment by a taxi driver and the deterioration in living conditions.
"We were better off 70 years ago," Fathy said in the video, adding that "women used to walk around in miniskirts and if someone was to even look at her, she could just call an officer and they would take him to court. It's infuriating — those that blame the way that women dress. Women dressed the same way 70 years ago. This didn’t happen then."
Charged with spreading false news, undermining national security and publishing an indecent video, Fathy was handed a two-year jail sentence and fined 10,000 Egyptian pounds (US$557) in September. However, the sentence was suspended pending an appeal.
Lotfy, the director of the Egyptian Commission for Rights and Freedoms, said authorities had never told Fathy what the charges were in the second case, in which she was accused of being a "member of a terrorist group" and other offenses.
She was released from pre-trial detention in the second case Thursday on condition that she checked into a police station once a week and only left her home for medical reasons, Lotfy said.
Amnesty International called the latest ruling an "outrageous injustice."
"The fact that a survivor of sexual harassment is being punished with a two-year prison sentence simply for speaking out about her experience is utterly disgraceful," the rights group said in a statement.
Fathy, who has a three-year-old child, is a member of the now banned April 6 youth movement, which played a role in 2011 mass protests that forced President Hosni Mubarak from office.
A United Nations survey in 2013 revealed that 99.9 percent of women in Egypt reported that they had experienced some form of sexual harassment in their lifetime. A 2017 Thomson Reuters poll described Cairo as the most dangerous megacity for women in the world.