Frank de Boer’s side outclassed their oponents from the start and cruised into a 2-0 lead at half-time through goals from Kolbeinn Sigthorsson and Christian Eriksen.
The second half followed much the same pattern as further strikes from Viktor Fischer, Siem De Jong and Danny Hoesen secured another domestic crown and condemned Willem II to relegation.
The result left the Amsterdam giants four points clear of nearest rivals PSV Eindhoven, whose 4-2 win over NEC Nijmegen was not enough to take the title race to the final round of matches.
It is the 32nd time Ajax have been crowned Dutch champions and coach de Boer becomes only the third man to lead them to three Eredivisie crowns in a row after Rinus Michels and Louis van Gaal.
De Boer also has the honour of becoming the first player to win the league title three consecutive times with Ajax and then repeat the feat as a manager.
Meanwhile, Sunday’s thrashing of Willem II by the Amsterdammers condemned their opponents to relegation.