Minamino ends a two-and-a-half year stay at Anfield, having joined from RB Salzburg in January 2020.
The Japanese international came to England with a big reputation but struggled to break into Jurgen Klopp's starting eleven, spending time on loan at Southampton in the second half of the 2020/2021 campaign.
In all, Minamino made 55 appearances for Liverpool, scoring 14 goals.
He is the third senior player to leave Liverpool this summer after Divock Origi and Sadio Mane, though the Reds have also brought in Darwin Nunez, Fabio Carvalho and Calvin Ramsay.
Speaking to his new club's official website, Minamino said: “It is a great joy for me to join AS Monaco.
“I am very happy to be part of this very exciting project, at a club with a great tradition and among the most recognised in Ligue 1.
“I’m looking forward to discovering my new environment and doing everything I can to help the team.”
Paul Mitchell, the club’s sporting director, added: “We are very pleased and excited to welcome Takumi to AS Monaco.
"He is a player we have known for many years and since his arrival in Europe, he has gained experience at the highest level, particularly in European competitions, and has won a number of titles.
“With his winning culture, his ability to play in various positions on the pitch and his status as a key player with his national team, we are convinced that Takumi will contribute to the development of our young team and help the group to achieve our goals.
“We are delighted that he has decided to be part of our project and welcome him.”
