The Italy international says he is "very proud" to have joined the Spanish champions after passing a medical and signing a three-year deal on Monday
The Italy international completed his medical early on Monday in the Spanish capital before signing a three-year deal after the two clubs agreed a fee over the weekend.
Cerci says he is "very proud" to have joined the league champions and believes he can continue to develop as a player under Diego Simeone.
"Atleti are a team that is still evolving and always wants to win, so I'm very proud to be here," the 27-year-old told the club's official website.
"I'm very happy for the great reception I've had. I hope that this season brings plenty of success. Atletico gave me a great opportunity and I want to show what I'm worth."
Atleti sporting director Jose Luiz Perez Caminero admits the club have gone to great efforts to bring in the likes of Cerci this summer to sustain their place at the summit of Spanish football but is confident their work will pay dividends.
"The agreement with Torino to sign Cerci is a joy for all of us," he said. "It was a clear objective for us to finish reinforcing our squad before we have to face the challenges that lie ahead this season.
"We have had to make a great effort after all the business we have done this summer, but we're convinced it was worth it because he will be a key piece for us this season. He provides an overlap, pace, goals... he will allow us more alternatives in our attacking game."
Cerci, who has notched 21 goals and 19 assists over the past two campaigns with Torino, was part of the Italy squad at this summer's World Cup.