The former AC Milan joined the Viola in a Bosman transfer last week.
“I had a few offers, I took time to think about my future and then immediately said yes to Fiorentina, because it's the ideal club for me," said Bonaventura at his presentation.
“There are a lot of quality midfielders in the team and that can help everyone stay on their toes. I always found there to be a great atmosphere in Florence, so when I received the call, I didn't have to think too long."
Bonaventura confirmed he has signed a two-year contract with option for a third.
“I wasn't upset that Milan didn't offer me a new contract, as I already knew in January that I'd be moving on. I tried to end the season in the best possible way, but I knew I was leaving.
“I had that moment after my final game at San Siro, alone on the pitch, because it was leaving a place after so many years. I wanted to feel the full sense of gratitude for all I'd achieved there.
“It's good to see Patrick Cutrone again, he's so fired up and I hope he can have a great campaign. I'd never met Franck Ribery, but you can tell within one touch of the ball in training what a champion he is. We're here to help the younger players to mature, much like what Zlatan Ibrahimovic brought to Milan."