He migrated to Australia with his family in 1950, and became an ironworker and active in the Federated Ironworkers Association, at that time controlled by the Communist Party of Australia. From 1952 Ducker was an official of the union under the new anti-Communist leader, Laurie Short (a non-Catholic). His characteristic North English accent led to him becoming known as "Broovver Dooker" throughout the movement.
In 1961 Ducker moved from the Ironworkers to the Labor Council of New South Wales, becoming first an organiser and in 1975 becoming Secretary.
He was also President of the New South Wales Labor Party and vice-president of the Australian Council of Trade Unions. In these positions he supported successive New South Wales Labor leaders such as Pat Hills, Neville Wran and Barrie Unsworth (also a Catholic convert).
In 1973 he was the main organiser of the leadership coup which replaced Hills as leader with Wran, who went on to become Premier of New South Wales for ten years. Ducker was also a powerful supporter of Federal Labor Leader Gough Whitlam in his battles with the left wing of the Labor Party during the 1960s.
In 1970 Ducker was a leading figure in the internal crisis in the Labor Party that cemented Whitlam"s leadership.
He had a long association with Mater Maria Catholic College
In 1979 Ducker"s health declined and he resigned all his official positions, but Wran appointed him Chairman of the New South Wales Public Service Board. He remained a powerful influence behind the scenes, supporting younger Labor leaders such as Graham Richardson, Bob Carr and Paul Keating. He was also appointed to several company boards, including Qantas and the poker machine giant Aristocrat Leisure Industries.
When the Labor Party split in 1955 over the related issues of Communism and the role of Santamaria"s "Movement" within the party, Ducker did not follow many other Catholic anti-Communists into the Democratic Labor Party, but remained in the Labor Party, becoming a leading figure in the party"s right wing.
In 1972 he was appointed a member of the New South Wales Legislative Council.