The Croatian, who joined Barca from Sevilla in 2014, has signed a three-year deal with the Europa League holders after being told he would be surplus to requirements at Camp Nou by new coach Ronald Koeman.
Rakitic enjoyed a hugely successful spell in Catalunya, winning the Champions League in his first season in 2015, but has gradually fallen out of favour over time, and was close to leaving in the summer of 2019.
But Sevilla sporting director Monchi has negotiated the player's return for an undisclosed fee and he will become their third signing of the summer after the arrival of Suso from Milan and Oscar Rodriguez from Real Madrid.
It is likely that he will take the place in midfielder of the departed Ever Banega, who played such a crucial role in their Europa League success over Inter at the end of last season and who left under the Bosman ruling.
Sevilla's first match of the season will be against Bayern Munich in the European Super Cup on 24 September.