Joseph McGarrity was born on March 4, 1874 in Carrickmore, County Tyrone, Ireland. He came to the United States at the age of sixteen and settled with relatives in Philadelphia. He engaged in various business enterprises in Philadelphia as well as in New York and Atlantic City and spent part of 1926 in Bogota, Columbia on business.

Overriding Joseph McGarrity's many interests was the cause of Ireland as a country free and independent of British control. He became a leader of the Philadelphia district of Clan-na-Gael and was a generous supporter of numerous organizations and individuals working for Irish liberty. McGarrity counted among his close friends Sean MacDermott, John McBride, Michael Collins, Harry Boland, Sean T. O'Kelly, Sean Russell, as well as many others. Padraig Pearse and Roger Casement stayed at his home while visiting Philadelphia. When Eamon De Valera came to America to raise funds for an Irish Republican government bond issue, he was in constant touch with Joseph McGarrity, whom he considered one of his most active and effective supporters.

Joseph McGarrity died on August 5, 1940 in Philadelphia.