Officially confirmed on Wednesday, the move ends months of pursuit by sporting director Fernando Soriano and returns the 29-year-old to Riazor for the first time since he left as a teenager for Manchester City.
The loan runs with a non-obligatory purchase option worth an estimated €2.5m, and comes as Deportivo La Coruna secure a left-back for their return to the Spanish top flight after eight years away. Angeliño will link up with Antonio Hidalgo's squad in Florence, where the club are holding their pre-season training camp, once his exit from Roma is finalised.
"There are stories destined to find each other again. That of José Ángel Esmorís Tasende, 'Angeliño', and RC Deportivo is one of them," the club said in a statement announcing the move, which included an emotional video reuniting the player with fellow academy graduate Loureiro, a team-mate from his formative years at the Escuelas de Fútbol Calvo Sanz in nearby Carballo before both progressed into Deportivo's youth system.
The club added that it "welcomes a player who never hid his desire to return."
Angeliño's journey away from Abegondo has taken in five of Europe's major leagues, with spells at Manchester City, PSV Eindhoven, RB Leipzig, Galatasaray and, most recently, AS Roma, in a career that has also included loan stints at New York City FC, Girona, Mallorca and NAC Breda.
His return fills Deportivo's most pressing need in defence, having relied solely on Quagliata at left-back following Sergio Escudero's departure, and adds significant top-level experience to Hidalgo's squad. He arrives with more than 300 senior appearances at the top level: 101 games and seven goals in the Bundesliga, 68 and four in the Eredivisie, 61 and two in Serie A, plus 29 Champions League appearances yielding three goals and 23 in the Europa League for another three.
The move follows a difficult campaign in Rome, where an asthmatic bronchitis diagnosis caused Angeliño's respiratory system to deteriorate into serious complications, sidelining him for close to six months and costing him around 30 appearances as well as considerable muscle mass; the club kept the details of his condition largely private throughout the most critical period.
He underwent a gradual rehabilitation process before returning to full training and first-team action in the spring, and has since passed a medical with Deportivo without issue.
"RC Deportivo has signed a top-level player with experience at the elite of European football, but has also recovered one of its own – a player who understands what this badge means, what this fanbase feels, and the responsibility of defending these colours," the club said.