The Brazil international returns to Camp Nou five and a half years after his previous eight-season stint with the Catalan giant came to an end, though he will not be eligible to play until January.
Alves won 23 trophies during his first spell with Barcelona before spending a season with Juventus, two seasons with Paris Saint-Germain and the past two years with Sao Paulo.
He was in attendance for Barca's 1-0 win over Dynamo Kiev on 3 November (AEDT) and the LaLiga side confirmed on Saturday (AEDT) that the 38-year-old is returning to the club as a free agent.
Two months after leaving Sao Paulo over a contractual dispute, Alves has put pen to paper on a deal with Barca that will run through until the end of the season.
Alves's return comes a week after club legend Xavi was appointed as Barcelona's new head coach, with his former team-mate reportedly playing a big part in the shock transfer.
The veteran defender made 247 appearances for Barca after joining from Sevilla in 2008, helping the club to six La Liga titles and three UEFA Champions League crowns during a hugely successful period.
He played his part in 95 clean sheets, had 78 goal involvements (64 assists, 14 goals) and created 377 chances, the latter total across the eight-year period beaten by only five players, two of whom were Lionel Messi and Cristiano Ronaldo.
The Bahia academy product captained Brazil to Tokyo 2020 Olympic Games gold in August, which he rated as his greatest achievement in a career that has seen him win 42 trophies in total at senior level for club and country.
Alves recently stated his desire to join a big-name club in order to regain his place in the Brazil squad, with the most recent of his 119 caps coming in September's 2-0 FIFA World Cup qualifying win against Peru.