The defender started his career in Barca's youth ranks before Arsenal brought him to the Premier League in 2011, where he went on to become a first-team regular.
However, after falling out of favour under Mikel Arteta, the London side agreed to terminate his contract with one year left to run and Bellerin returned to Barca on a free transfer.
The 27 year-old has now left the Spanish giant for a second time, though, having made just seven appearances in all competitions since rejoining in September.
While Sporting's Primeira Liga title hopes look over, Bellerin will hope to help his side in the Europa League, with the club due to face Midtjylland in the knockout round in February.
Bellerin's arrival at the Portuguese side comes as fellow attack-minded right-back Pedro Porro departs the club for Tottenham.