The Dutch titleholders confirmed on Friday the coach, and his assistant, Hennie Spijkerman, have committed themselves to the club for a further four years
The former Netherlands international had already verbally agreed last month to extend his stay in Amsterdam for a further four years, but he only signed on Friday.
Ajax also confirmed on their official website that assistant coach Hennie Spijkerman has also committed himself to the club until June 30, 2017.
De Boer, who spent 11 years at Ajax as a player, has led the Dutch giants to three successive domestic titles since being appointed coach in the summer of 2010.
The 43-year-old previously was in charge of Ajax's youth team before returning to the Amsterdam ArenA in 2010 after a stint as an assistant coach with the national team.