Juve released a series of pictures and videos on its official Twitter account showing De Ligt arriving for his medical.
He scored against Juventus as the 34-time Dutch champion upset the odds to reach the Champions League final four, and the season before become the youngest player to star in a European final when Ajax lost to Manchester United in the Europa League.
De Ligt follows former Ajax teammate Frenkie De Jong — who signed for Barcelona earlier this year — as another of the club’s youth products sold to one of Europe’s top clubs.
He joins the Italian champion under newly-installed manager Maurizio Sarri, who has moved to Juventus after a season at Chelsea, and will play alongside experienced defenders Giorgio Chiellini and Leonardo Bonucci.