The prolific Porto striker looked set to join Milan earlier this month before performing a U-turn and agreeing a switch to la Liga.
And the Colombia international, who made his first start of this month’s Copa America last night as he team were defeated on penalties by Argentina, has revealed he has agreed a four-year deal with Diego Simeone’s side and hopes to have as big an impact as compatriot Radamel Falcao did at the Vicente Calderon.
“I can confirm I am going to Atletico,” Martinez told reporters in Vina del Mar.
“I am going there for four years, but I still don’t know when I will be introduced.
“I have had a great progression, always learning, always growing, and now I'm going to Atletico where I hope to help the team and also continue to grow as a player.
“I hope to be another Colombian as successful as Falcao was there.”
The 28-year-old, who joined Porto from Mexican club Chiapas in 2012 and scored 21 league goals last season, will cost the Spanish club €35 million.