The once-capped Spain international has penned a one-year contract with the Rojiblancos and is looking forward to competing with Thibaut Courtois for the No. 1 jersey.
The 33-year-old goalkeeper completed a medical in the Spanish capital on Tuesday morning before signing a 12-month contract with the Rojiblancos.
Aranzubia grabbed the headlines in February 2011, when he became the first goalkeeper in La Liga history to score from open play, heading home a 95th-minute equalizer against Almeria.
Aranzubia freely admitted that he knows he faces a difficult task in trying to usurp Thibaut Courtois as Atletico's first-choice goalkeeper, but he insisted that he was looking forward to the challenge.
“I am delighted to be joining such a massive club,” Aranzubia told reporters. “I’m really happy and cannot wait to start work.
"I know that Atletico already have a great goalkeeper but I have come here to focus on what I need to do.
"I have to compete for a place and help the team to do well."
Aranzubia, who has one Spain cap to his name, had spent five seasons at the Riazor after joining from Athletic Bilbao in 2008.