He was born in New York to immigrant parents from County Sligo, living first in west Harlem before moving as a child to Mott Haven in the Bronx.
McGann received violin instruction from Catherine Brennan Grant, a teacher grounded in both classical and Irish traditional music, and played in parochial school orchestras.
At a very young age, McGann found a place among the elite of New York's Sligo-style fiddle players, including Coleman, Paddy Killoran, Martin Wynne, Louis Quinn and James "Lad" O'Beirne.
With Reynolds and others, McGann played with The New York Céilí Band, an all-star group that traveled to Ireland in 1960 to compete at the All-Ireland fleadh cheoil in Boyle, County Roscommon.
McGann's first studio recording was the 1965 LP A Tribute to Michael Coleman with button accordionist Joe Burke and piano accompanist Felix Dolan.