They wrapped up the league with a thumping win over Heerenveen at the Johan Cruyff Arena.
It sent them four points clear of nearest rivals PSV Eindhoven before Sunday's final round of games.
Ajax's scorers were Nicolas Tagliafico, Steven Berghuis, Sebastien Haller, Brian Brobbey and Edson Alvarez.
It was a fitting farewell for Ten Hag, who United announced in April as their next manager.
The Dutchman, 52, will take over from interim boss Ralf Rangnick at the end of this season on a three-year deal, which can be extended by a year.
Ten Hag will become United's fifth permanent manager since Sir Alex Ferguson retired in 2013.
He took over as Ajax head coach in December 2017 and led them to the league and cup double in 2018-19 and 2020-21.
However, they were beaten 2-1 by PSV Eindhoven in this season's Dutch Cup final.
