The 20-year-old, who made 28 appearances for the Gunners during the 2017-18 campaign, has also been handed the number 15 shirt for the new season.
Maitland-Niles has played left-back, left midfield and central midfield since making the breakthrough into the first team, and his future at the Emirates Stadium has now been secured.
"Ainsley Maitland-Niles has signed a long-term contract extension with the club," read a statement on Arsenal's official website.
"Joining our academy at the age of nine, he enjoyed another successful season, featuring regularly for the first team in 2017/18. He made 28 appearances during the campaign at wing-back or full-back and in midfield."
Maitland-Niles appeared in 15 of Arsenal's 38 Premier League matches during the 2017-18 campaign.