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. Shortly thereafter MacGinty moved back to Ireland as he was signed to play professionally for Connacht in the Celtic League, commonly known as the Guinness PRO12, for the 2015-2016 season.
MacGinty made his domestic debut for Connacht appearing off the bench in their 33–19 win over Benetton Treviso on November 6th, 2015. Eight days later, MacGinty made his European debut in the first match of the 2015–16 Challenge Cup, starting at fly half and scoring nine points. MacGinty led Connacht to a 28–23 bonus point win over Edinburgh in March 2016 and, as Alan Lorimer of The Irish Times put it, "controlled matters expertly."
All of this culminated with Connacht making history for the very first time in their 121 years of existence as they would win their first major championship by defeating, European and Irish powerhouse, Leinster by a score of 20-10. MacGinty played all 80 minutes and "carried out the ambitious game-plan with calm assurance," said Ruaidhri O'Connor, reporter for The Irish Independent.
In May of 2016, it was announced that MacGinty would join the English Premiership Sale Sharks to replace outgoing fly half, Danny Cipriani.