His previous deal had been due to expire next year, meaning the extension secures one of the club's most experienced defenders for a further period at the heart of their backline.
AS Roma announced the news alongside a second contract extension for midfielder and team captain Bryan Cristante, 31, who has signed a new deal running one year shorter than Mancini's, through to 2028. The two announcements came together, underlining the club's determination to lock down key figures within the squad ahead of the new season.
Mancini has established himself as one of the more reliable defensive presences in Serie A during his time in the capital, becoming a regular fixture in Roma's backline across multiple head coaches and tactical systems.
His new deal ensures continuity at the back for a club that has placed a premium on retaining experienced, homegrown-feeling figures within the squad even as it continues to invest in fresh signings elsewhere.
Cristante, meanwhile, extends his own lengthy association with the club as captain, a role that carries significant symbolic weight at a club with Roma's history and fanbase.
Both extensions reflect a broader summer strategy of prioritising squad stability and continuity around senior figures, giving Roma's coaching staff a settled core to build around as they prepare for another demanding campaign across domestic and European competition.
Head coach Gian Piero Gasperini, who arrived from Atalanta last summer and guided Roma to a third-placed finish and a return to the Champions League, has been clear that he sees this Roma squad as one to build on rather than overhaul, and the extensions for Mancini and Cristante fit that philosophy directly.
Both players have remained trusted figures under Gasperini, who has previously praised the technical and leadership qualities several of the club's senior players bring to a dressing room already blending experience with emerging talent such as Niccolò Pisilli, as Roma prepare for a season that will also include a Supercoppa Italiana semi-final against Napoli in December.