He attended Christian Brothers College, St Kilda.
[1] After obtaining a diploma of commerce from the University of Melbourne in 1927, he moved to Canberra.
[2] In 1934, Halligan participated in the first air mail flight to New Guinea, captained by pioneer aviator Charles Ulm.
[5] As an adviser, Halligan was freed from routine administration work to focus primarily on United Nations Trusteeship Council matters.
[7] Halligan was made an Officer of the Order of the British Empire in 1960.