As reported by Flashscore, Smalling underwent the usual medical examinations on Wednesday and signed a contract with Porto valid until the end of the season, with an option for another year.
Born in Greenwich, southeast London, Porto's new number six started playing football on the outskirts of the English capital and was also part of Millwall's squad before joining the youth ranks of Maidstone United, a club in the lower tiers of British football based in Kent.
After impressing in his first games as a senior player, he received an offer from Fulham, which opened the doors to the English League and European competitions.
In his second season at Craven Cottage, Smalling helped the Londoners reach the Europa League final and eventually moved north.
Having just signed for Manchester United, Smalling won the English Super Cup on his official debut and became a national champion in his first months under Sir Alex Ferguson.
Another Super Cup victory followed before his long-awaited debut for the English national team, under Fabio Capello, in a Euro 2012 qualifying match.
In his nine seasons at Old Trafford, the 31-time England international centre-back wore the Manchester United shirt on 324 occasions, scored 18 goals and won two Premier League titles, one Europa League, one FA Cup, one EFL Cup and three Community Shields.
In between, he was named to the Europa League Team of the Year in 2016/17 and was a starter for England at the 2014 World Cup and Euro 2016.
In the summer of 2019, Smalling embarked on his first international adventure, signing for Roma, a club he represented for five seasons, winning another international title and earning a place in the 2021/22 Conference League Team of the Year.
Over the last two seasons, the 36-year-old centre-back was coached by Pedro Emanuel at Al Fayha in Saudi Arabia, making 56 appearances under the former Porto defender.
With 31 caps for England and a curriculum full of titles, Smalling is preparing to broaden Francesco Farioli's options in the back line.