Borini confirmed his decision on social media on Wednesday after his contract expired this summer.
He began at Bologna before joining Chelsea’s academy aged 16 in 2007.
The forward later represented Roma before earning a €13.3 million move to Liverpool in 2012, the same year he made his only senior appearance for Italy.
Borini also played for Sunderland, Swansea City, Parma, AC Milan and Hellas Verona during his career.
"It all started with a flight. Thank you, Chelsea. I was 16 years old. A flight I spent entirely with tears in my eyes, beginning the journey of my career with no real destination, other than the dreams I wanted to achieve,” he wrote on Instagram.
“From that day on, I started building myself, without knowing what would become of that kid with such a strong mindset. I started building my dreams in my head, and somehow, I ended up turning them into my reality.
“The same reality that today will change forever. The reality that has shaped my past, my present and my future. Today, just like that day when I sat on a plane to London, I feel those same emotions about what lies ahead.
“Fear. Happiness. Courage. Uncertainty. Dreams. Success. Passion. Sacrifice. I want to thank that kid who never stopped believing. And the man I am today will keep believing in the next opportunity, this time without a ball at my feet, but with that same belief. Always. Thank you, thank you, football.”