Alexandre Benalla was fired after video of the May Day incident emerged – Emmanuel Macron’s first major political crisis.
Benalla was given a three-year term but will not go to jail, as two years were suspended and he will serve the third wearing an electronic bracelet.
The former aide had denied the charges, saying he acted to help officers.
The video showed Benalla, wearing a police helmet, striking a young man and grabbing a young woman by the neck during the protest in Paris. It later emerged Benalla had been given permission to attend the disturbance as an observer on his day off.
The presidency was accused of a cover-up for not acting on the case as it knew of the existence of the video. It only acted after newspaper Le Monde identified Benalla.
Benalla, now 30, played an important role in Emmanuel Macron’s presidential campaign.
He rose through the ranks of the Elysée and was regularly seen in public at the president’s side.
The court also found him guilty of illegally using his diplomatic passports after his dismissal, of having forged a false document to obtain an official pass, and of illegally carrying a weapon in 2017.
He was also fined €500 (£430; $575).
The sentence was greater than the 18-month suspended term sought by prosecutors.