Lopez, who plays for Barcelona's Under-16s team, has turned down a new contract offer from the Spanish champions, who were understood to be desperate to keep him at La Masia.
The 16-year-old left-back has been at Barcelona since the age of seven, but Sport reports that he is hopeful a move away from Catalonia will improve his playing prospects.
Arsenal's head of recruitment Raul Sanllehi is understood to have been integral to completing the deal, having left Barcelona for Arsenal at the start of the year.
The Gunners will only have to pay a compensation fee for Lopez's signature due to the teenager being out of contract at Barcelona.
Arsenal have also been linked with another highly-rated youngster this summer, closing in on Paris Saint-Germain's Yacine Adli.