The 19-year-old centre-back had been linked with a number of Europe’s top clubs but completed a £67.5m move to the Italian champions on Thursday.
Former Chelsea boss Sarri was unpopular with some supporters at Stamford Bridge and left the club earlier this summer after less than a year in charge.
“He was one of the reasons that I wanted to join here,” said De Ligt.
“I spoke to Sarri on the phone before coming just to get to know each other.
“I’ve heard a lot of good things about him and I like his footballing philosophy and how he prepares his defence.”