The deal is reportedly worth €33.5 million with an additional €5 million in add-ons.
Merino is expected to travel to London today (Friday 23 August) to undergo a medical and finalise the terms of his contract, which is set to be for four seasons with an option for an additional year.
The official announcement is expected shortly after these formalities.
The deal was sealed during a second face-to-face meeting in London, led by Jokin Aperribay, president of Real Sociedad.
Although the Spanish club initially sought around €40 million, they ultimately agreed to a slightly lower fee given Merino’s contract situation. His current deal with Real Sociedad was set to expire next summer and the player had already expressed a desire to join Arsenal.
Merino, who has missed Real Sociedad’s last two training sessions due to the transfer, is now set to start a new chapter in his career with Arsenal.