This paper investigates the impact of the thermally induced deformation of soil on the serviceability mechanical performance (i.e., deformation-related) of energy pile groups. The work is based on the results of a full-scale in-situ test that was performed over a typical time-scale of practical applications on a group of energy piles at the Swiss Tech Convention Centre, Lausanne, Switzerland, and on a series of 3-D thermo-mechanical finite element analyses that were carried out to predict the considered experiment. This study proves that the serviceability mechanical performance of energy pile groups crucially depends on the thermally induced deformation of soil. Considering this aspect in the analysis and design of energy piles is important because it profoundly characterizes the deformation of such foundations.