Although he and a colleague were charged with conspiracy, they were found not guilty, and Conroy continued his union career.
After a period working in Limerick, he moved to Dublin to take charge of the union's Industrial Section.
He served as ITGWU vice-president from 1946 to 1953 and general president from 1953 to 1959 and 1968 to 1969.As President of the union, Conroy focused on a programme of modernisation, along with campaigning for a national minimum wage.
He also worked with James Larkin Jnr, to promote the merger of the Irish Trade Union Congress and the Congress of Irish Unions, which was accomplished with the founding of the Irish Congress of Trade Unions in 1959.
This accomplished, Conroy served as the first president of the new organisation, and discussed a merger of the ITGWU with Larkin's Workers' Union of Ireland, although this did not occur until many years later.