The 27-year-old defender, who joined United from Sampdoria last summer, has featured in eight of his side's opening nine fixtures this campaign.
Having now become a key component in the Whites' starting lineup, Berardi has agreed to prolong his stay in Yorkshire by agreeing fresh terms.
"I'm very happy here," he told the club's official website. "The city and everything is very good. We are a team this season after many changes last season. We are a very good group together - that is important.
"Last season the first two or three months were difficult for me and for the other new players. This time I started the pre-season and that is very important. My body is better and I feel fitter.
"I have been playing right-back, which is my position. We are playing well with the full-backs in every game. I hope to stay in this position through hard work every day and hard work every match."
Berardi featured 24 times for United in all competitions last season after securing a regular place in the team at the turn of the year under former coach Neil Redfearn.