For a number of months, it has been claimed that the former Chelsea player had agreed to move to Camp Nou upon the expiration of his contract at Stamford Bridge.
However, despite no transfer fee being involved, the Catalan giants have been required to ease their financial issues before officially confirming the acquisition of the Denmark international.
The La Liga side have now followed suit by formally announcing that Christensen has become a Barcelona player on a contract until 2026.
Barcelona have also revealed that Christensen, who will be presented to the media on Thursday, will have a release clause of €500m (£430.2m) in his deal.
Christensen spent a decade in West London, initially featuring in the academy setup before becoming a first-team player at the Premier League club.
The majority of his 161 appearances came after a two-year loan period at Borussia Monchengladbach, where he featured on 82 occasions between 2015 and 2017.
While Christensen failed to win a Premier League title with Chelsea, the 26-year-old played a key role as his team won the Champions League during 2020-21.
The latter is most most likely to return to his homeland, head coach Thomas Tuchel said to have given the green light for Alonso to end his period at the club.
However, the situation with captain Azpilicueta appears to be more complicated with Tuchel allegedly wanting to retain the services of the legendary full-back for another 12 months.