Hesz takes up the post this month, and will oversee the agency's digital activity and enhance its social media offer.
Adam & Eve already works with a number of brands on digital activity, including Halifax, Foster's and Phones4u, and earlier this year was appointed by JK Rowling and Sony to promote the Pottermore website that is based on the Harry Potter series.
Hesz worked at Modernista! for just over a year, and was responsible for helping the agency create web campaigns for the retailer Sears and the TV show Dexter.
Before moving to Boston, Hesz worked in the UK, spending time at agencies including M&C Saatchi, Bartle Bogle Hegarty and DDB London, where he ran the agency's Nestle UK business.
Hesz also published his first book, Guilt Trip, in 2009 which explored the role of fear and guilt in modern marketing.
Hesz said: "This is a chance to lead a group of talented people with the desire to produce work that not only works beautifully but answers real consumer and client needs."