The Leicester City midfielder joined on loan with a €10m option to buy.
“I signed right at the end of the window and Monday was a stressful day," the Algeria winger said at his official unveiling.
“My agent told me about the Viola, I immediately said 'yes' and then I just waited for the two clubs to reach an agreement.
“When it was reached, I breathed a sigh of relief. I'm a technical player, I like to get past my man and dribble.
“I feel comfortable starting from the right, even if I'm left footed. I hope I can give my best to help Fiorentina.
“My year at Leicester was a complicated one, so when a historic and mythical club like Fiorentina called me, I took a chance that I didn't want to miss out on."