After attending St. Patrick's College, Wellington, McCarthy moved to Hāwera, where he qualified as a lawyer and in 1903 founded the law firm that is now known as Welsh McCarthy.

[1] He became president of the St. Patrick's College Old Boys' Association; for his work for the Old Boys and for organising the school's golden jubilee celebrations in 1935 he was awarded the papal knighthood of St Gregory the Great.

[2] McCarthy played four matches for Taranaki during its brief period as a first-class cricket team.

In Taranaki's only first-class victory, against Hawke's Bay in 1896–97, he took 3 for 42 and 4 for 46 with his off-spin.

[3] Hawke's Bay reversed the result in their next encounter in 1897–98, although McCarthy took his best figures of 5 for 109 and top-scored in each innings with 27 and 52, his best first-class score.