Gerndt, the top scorer in the Allsvenskan last season, follows fellow Swedes Johan Martensson and Marcus Nilsson to the Galgenwaard Stadium.
A host of European sides, including West Brom, Blackburn and Fulham, were thought to be interested in the 25-year-old, but Utrecht have won the race for his signature.
The Sweden international will delay his arrival at Utrecht until August 1 so he is available to play for Helsingborgs in the first leg of their third round Europa League qualifying clash on July 28.
Utrecht chairman Jan Willem van Dop told the club's official website: "I must say that we have a very successful period (of transfers) behind us.
"We had our sights focused on three players and we have signed all three.
"For the three Swedes, but especially Gerndt, there was also much interest from other clubs, but thanks to the decisive and the good 'story' of FC Utrecht they have chosen our club.
"The boys are stable, strong personalities and they saw the outlook that FC Utrecht offers. They have chosen our approach, our system.
"This means that a move to FC Utrecht can mean a great step toward the next big step."