A graduate of Blackrock College, MacGinty played with the Blackrock College RFC academy before moving to New York on a visa where he began playing with the New York Athletic Club. In 2012 MacGinty moved to Marietta, Georgia, where he began a master's degree in Sport Health Science and excelled on the rugby pitch at out-half for the Life Running Eagles.
MacGinty made his debut for the United States in July 2015 against Samoa during the Pacific Nations Cup. In the U.S. team's last match of the 2015 Pacific Nations Cup against Canada, MacGinty scored all of the team's points, including a last minute drop goal, to win the match 15–13. MacGinty was the U.S. team's leading scorer throughout the 2015 Pacific Nations Cup, scoring 44 points in three matches.
Following his performances in the Nations Cup, MacGinty was named in the American squad for the 2015 Rugby World Cup. He featured in three of the team's four games, starting in each of his appearances and scoring 25 points.
In May of 2016, it was announced that MacGinty would join the English Premiership Sale Sharks to replace outgoing fly half, Danny Cipriani.