Ralph was born in Newcastle, New South Wales on 30 September 1909, the son of Hugh Marsh and Jane Ann, née Benson.
His father was a marine engineer for the Department of Public Works, and Ralph was raised and educated at Nambucca Heads, New South Wales.
Marsh (who converted to Catholicism following his marriage in 1933) was elected to the central executive of the New South Wales branch of the Labor Party in 1952 with the support of the 'Groupers'.
[3] In 1957 Marsh was elected as an organiser for the Labor Council of New South Wales, the peak representative body for trade unions in the state.
During this time he also served on the executive of the Australian Council of Trade Unions, including a period as junior vice-president.