Timber has 15 senior international caps and is believed to have been signed predominantly to play at right-back for Mikel Arteta’s side.
He has been a long-term target for Arsenal, with his ability on the ball and his pressing already aligned with what Arteta is aiming to achieve.
Timber has two Eredivisie trophies to his name and was part of the Dutch side that won the European Under-17 title in 2018.
He played under Manchester United boss Erik ten Hag at Ajax and had been linked with a reunion last summer before putting pen to paper at the Emirates Stadium.