Born in Sydney to Thomas James Scully and his wife Sarah Lucy Rutherford, he was educated at a small school near Tamworth.

After three unsuccessful attempts to enter the New South Wales Legislative Assembly, he succeeded his brother Patrick,[3] in the electorate of Namoi in 1923.

Although he agreed with many of the views of New South Wales Premier Jack Lang, Scully remained loyal to the Prime Minister, James Scullin, and to the Australian Labor Party.

He held this position under Curtin, Frank Forde and Ben Chifley, and chaired the Australian Food Council.

"The Scully Plan", which aimed to guarantee wheat farmers a minimum price of four shillings per bushel, was introduced in 1942.