Gamez moves to Estadio Vicente Calderon after spending his entire career with Malaga.
The 29-year-old made his debut for the Andalusians against Getafe in 2005 and will now look to become a regular with the reigning Spanish champions.
With the ability to play in the centre of defence or on the right, Gamez brings versatility to a side who have lost the services of left-back Filipe Luis and right-back Javier Manquillo in the transfer window.
And Atleti are confident that Gamez will be a strong addition to Diego Simeone's squad.
"Gamez is a full-back with quality and experience who will reinforce our defence and increase the group's internal competitiveness," Atleti's sporting manager Jose Luis Perez Caminero told the club's official website.
"He can also play in a central position, allowing us to have other variables in the defensive game. His experience will be helpful to the group."
Atleti begin the defence of their title at neighbours Rayo Vallecano on August 25.
