Ahead of the 2014–15 season, Masterson was made captain of the Eagles and started all six of Connacht's matches in the 2014–15 British and Irish Cup. As in the previous season, injuries to first team players meant Masterson featured for the senior team in the league. He made nine appearances, seven of them starts, and scored his first try for the first team against Newport Gwent Dragons on 22 February 2015, adding two more during the campaign. On 3 April 2015 Masterson made his European debut, starting against Gloucester in the 2014–15 Challenge Cup quarter-final. Masterson also appeared in Connacht's final game of the season, also against Gloucester, in a play-off to qualify for the following season's Champions Cup, the top tier rugby competition in Europe. Connacht were beaten after extra time, by a score of 40–32. During the course of the season, Masterson signed his first senior contract with the province, a deal that lasts until summer 2017.