The Danish defender's new deal runs until the summer of 2028.
Christensen, 30, joined the Catalan giants in the summer of 2022 but had been playing on an expiring contract this season, leaving his future at the club uncertain.
Reports emerged over the winter that Barcelona wanted to extend his deal, and the two parties have been negotiating for some time since.
Christensen is understood to have turned down at least one contract proposal, but it had recently been reported that an extension was close.
The centre-back received relatively frequent playing time during his first two seasons at the club, but the past two years have been disrupted by injury problems.
Since his arrival, Christensen has scored five goals and provided three assists in 98 competitive matches for Barcelona, forming part of a defence that has won multiple domestic honours during his time at the club.
Christensen made his name at Chelsea, for whom he also had a two-year loan spell at Borussia Monchengladbach, before joining Barcelona on a free transfer in 2022.
During his time in England, the defender won the FA Cup, the Europa League and the Champions League with Chelsea, establishing himself as one of the club's most reliable defenders before his departure.
Christensen has won 82 caps for Denmark, scoring four goals and providing two assists at international level for his country.
He has represented his country at multiple major tournaments, including the 2018 and 2022 World Cups and Euro 2024, starting regularly for the Danes in central defence.
Last autumn, it was reported that Italian giants AC Milan and Saudi club Al Nassr were showing interest in the defender.
His versatility as a centre-back has been valued by successive coaching staff at Barcelona, even during periods when injuries have limited his availability over the past two seasons.
The extension ends any uncertainty over Christensen's immediate future at the club and represents a vote of confidence from Barcelona in a player who has struggled for fitness in recent seasons.
With his future now resolved, Christensen will be able to focus on returning to full fitness ahead of the new campaign after missing significant chunks of the past two seasons through injury.