Smalling's previous contract was set to expire at the end of this month.
The 33-year-old initially joined Roma on loan from Manchester United in the summer of 2019 before making the move permanent a year later.
The former Fulham defender has made 143 appearances in total for Roma, scoring ten goals and winning the inaugural Europa Conference League in the 2021/2022 season.
Smalling missed out on another continental title with Roma in the just ended season when Jose Mourinho's side lost to Sevilla on penalties in the Europa League final.
In an interview on the club's YouTube channel, he said: 'For me it's an easy decision because the last few years have been one of the best parts of my career. The support is incredible every time I go to walk my dog or go to the supermarket.
'Everything is so complete here that it was, like I said, an easy decision to stay for myself, for footballing ambition, as well as for my family. It's just the perfect choice for me.
'I feel fitter than ever. I'm feeling like I'm recovering from games and I was able to be part of many games this season (...) hopefully I will become better and keep improving.'
AS Roma general manager Tiago Pinto added: “During his time at the club, Chris has distinguished himself not only for his performances on the field but also for the sense of belonging he has shown, which has led him to tie his future to the club.”
“We are delighted to be able to count on both his defensive prowess and his leadership skills. He is a key dressing-room figure and a role model for the younger lads in our squad.”
