The Citizens have confirmed reports that emerged on Tuesday revealing that Begiristain will step down from his position at the end of the season.
Begiristain originally planned to step back from day-to-day operations at Man City when he turned 55, but he became so invested in the club's project and working alongside manager Pep Guardiola that he extended his stay until his 60th birthday, which he celebrated in August.
The Spaniard joined the reigning Premier League champions in 2012 in a move that reunited him with CEO Ferran Soriano, who he worked with during a successful spell at Barcelona.
Begiristain also worked closely alongside close friend Guardiola and has been an integral architect of Man City's rise to dominance in English football, with the club winning a total of 22 trophies across seven different competitions.
Viana to replace Begiristain at Man City next summer
His decision to leave was made with full knowledge and endorsement of Man City's hierarchy, and the club have now confirmed that the Spaniard will continue with his duties, in collaboration with Viana, until mid-July "to ensure a smooth transition".
A statement from Man City released on their official website read: "Manchester City can confirm that Txiki Begiristain will step away from his full-time role as Director of Football at the end of the 2024-25 season.
"Following a trophy-laden twelve years at the Etihad Stadium, Txiki will leave his current post following the club's involvement in this summer's FIFA Club World Cup and will be succeeded by Hugo Viana of Sporting CP.
"Viana will begin his full-time role in the summer of 2025, but will collaborate with Txiki in the preceding months to ensure a smooth transition.
"We look forward to paying tribute to Txiki's outstanding contribution to Manchester City at the end of the season."
Man City secure services of 'favourite candidate' Viana
Viana, who was identified as Man City's 'favourite candidate' to replace Begiristain, will depart his role at Sporting after six years as director of football with the reigning Primeira Liga champions, where he has gained sizable recognition for his work behind the scenes in his native Portugal.
The 41-year-old, who represented the likes of Sporting, Newcastle United and Valencia in his playing days, has overseen a number of high-profile outgoings at Sporting, with Bruno Fernandes, Manuel Ugarte, Pedro Porro and Matheus Nunes - now at Man City - among those who have departed for significantly higher fees than they were signed for.
In terms of incomings, the likes of Morten Hjulmand, Ousmane Diomande and Viktor Gyokeres - Sporting's goal machine who has recently been linked with Guardiola's side - are among those who currently star in Ruben Amorim's first-team squad.
Man City and Sporting will face one another at Estadio Jose Alvalade in the Champions League on November 5.