The Uruguay international, who was called up by Marcelo Bielsa for this year's World Cup without playing a minute, chose Deportivo's proposal ahead of interest from Sevilla and Valencia.
Giménez arrives at Riazor to bring experience to a Deportivo defence that has repeatedly struggled from set pieces in recent seasons, joining the newly promoted side without a purchase option attached to the deal.
Now 31 and increasingly overtaken in Diego Simeone's pecking order, Giménez made 16 league appearances and featured six times in the Champions League last season, still a player of genuine standing despite his reduced role at the Metropolitano.
Atletico Madrid have agreed to extend his contract by a further year as part of the arrangement, a mechanism designed to offset the wages he will earn in Galicia while Deportivo take on only part of his salary.
The move follows a wider reshuffle at Deportivo, where several players including Jurado, Puerto, Patiño, Comas and Barcia left the club to free up space and financial headroom for incoming signings. Head coach Antonio Hidalgo had made clear those departures were necessary to accommodate the kind of experienced reinforcement Giménez represents.
For Atlético, the exit reflects a squad increasingly reshaped around younger options in central defence, with Giménez's influence in Simeone's matchday plans having steadily diminished over recent campaigns. His arrival in Riazor gives newly promoted Deportivo a defender who has faced the club many times before, offering the kind of hierarchy Fernando Soriano's project has targeted throughout an ambitious summer of recruitment.
Giménez has made more than 370 appearances for Atlético since arriving from Danubio in 2013, becoming a key figure in Simeone's defensive system for the best part of a decade before injuries and squad competition began to limit his opportunities.
His move to Galicia represents one of the more eye-catching pieces of business in a summer that has already seen Deportivo La Coruna bring in Pierre-Emerick Aubameyang, Angeliño and Adama Traore as they aim to establish themselves back in the top flight after years outside it.