He served as premier of New South Wales from 1947 to 1952, holding office as leader of the Australian Labor Party (ALP).

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.

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.