The contract was previously held by the Aviareps Group in Germany.
PRWeek reported in August that the HTA had sent out an RFP, with the contract worth up to $800,000 (£516,000) for the first year.
Hills Balfour will start working for HTA from 1 January 2016. The brief is to promote Hawaii’s picturesque islands, increasing awareness of the destination across Europe through sales, marketing and public relations; boosting both leisure and business tourism.
The agency will cover the UK and Scandinavia markets in-house. Hills Balfour has sub-contracted partner agency Lieb Management in Germany to assist with the German and Swiss markets, and partner offices Interface Tourism in France and AIGO in Italy, to support in those markets.
Amanda Hills, CEO of Hills Balfour, said: "We are absolutely thrilled to be working with HTA again. Having held the HTA marketing contract for the UK between 2005 and 2008, we already have deep and insightful experience of Hawaii as a tourism destination.
"The Hawaiian Islands are an incredibly exciting and aspirational long-haul destination for the European market, and we are delighted to be acting as their European representative, taking them to the next echelon."