Mkhitaryan crowned a successful three-year spell at Roma with victory over Feyenoord in the Europa Conference League back in May.
The 33-year-old joined the Giallorossi initially on loan from Arsenal in the summer of 2019, going on to make 117 appearances, scoring 29 goals and assisting 26 times.
"Roma is a truly unique club," the former Armenia international said in an open letter.
"Your support has been outstanding and I will always be very proud of it.
"When I wore this shirt for the first time, I had a goal: to make this club win and to make its fantastic fans happy. Goal achieved in Tirana!
"This triumph was the perfect conclusion to my three years in the Giallorossi. Now it's time to say goodbye.
"I want to thank all the people who work in the club for the special relationship built together over the years.
"A huge thank you to our technical staff and in particular to Mr. Mourinho for his trust and attention towards me and for the extraordinary motivations he gave me as a player.
"I gave my all for Roma on and off the pitch. It was a great honour to play here and I will never forget the amazing moments we had together.
"This club and the Eternal City will remain forever in my heart. I love you!"
Mkhitaryan has signed a two-year contract with Inter and becomes the club's fourth summer signing after Romelu Lukaku, Andre Onana and Kristjan Asllani.
