The federation was established on 16 June 1925, at a meeting attended by representatives of unions from Belgium, Denmark, France, Germany, the Netherlands, Norway, Spain, and the United States.
It set up headquarters in Antwerp, and successfully negotiated representation on the Joint Maritime Commission of the International Labour Organization.
The International Transport Workers' Federation (ITF) had also evacuated to London, and it began working closely with the IMMOA.
Becu was seconded to ITF work, and the British Navigators' and Engineering Officers' Union took over the leadership of the federation.
It recommended that all its affiliates join the ITF, and refocused its activity on promoting friendship and co-operation among ships' officers.