Educated mostly at St Stanislaus College, Bathurst, he was later apprenticed to his brother Greg McGirr, a pharmacist at Parkes.

Employed by Washington H. Soul Pattinson in Pitt Street, he later opened a pharmacy in Parkes, specialising in veterinarians' prescriptions.

[1][2] McGirr followed his brothers Greg and Patrick into ALP politics and joined the Parkes branch of the party in 1906.

In 1922, Greg vacated his seat as a member of the Legislative Assembly for Cootamundra, and stood successfully for a Sydney electorate.

Due to local party opposition in 1925, he was obliged to find another seat in 1925; and he successfully contested Cumberland in western Sydney.

Decent, humane, well-liked, and personally free from corruption, McGirr as Premier was a great procrastinator, and delayed many proposals.

Even after the ALP won the 1947 state election, McGirr proved unable to increase significantly the representation of his supporters in the Cabinet as a whole.

[3] An ambitious public works program, which McGirr had promised in the 1947 campaign, was disrupted by post-war shortages and strikes.

The 1950 election produced such a big anti-ALP swing that it left the government depending for its survival upon the votes of two of the disendorsed members, who had won their seats as independents.