Tewson succeeded Walter Citrine as General Secretary of the TUC in 1946, supporting the post-war economic recovery of Europe, and assisting in creating a trades union advisory Committee for the Marshall Plan. In 1949 he was the secretary of the conference at Geneva during which the International Confederation of Free Trade Unions (ICFTU) was created, and served as its President from 1951 to 1953.
Tewson succeeded Walter Citrine as General Secretary of the TUC in 1946, supporting post-war economic recovery in Europe and assisting in establishing a trade union advisory committee for the Marshall Plan. In 1949 he was the secretary of the conference at Geneva where the International Confederation of Free Trade Unions (ICFTU) was created, and served as its president from 1951 to 1953.