He served in the Army during World War I, being commissioned as a second lieutenant in the West Yorkshire Regiment on 1 August 1917.[3] On 4 February 1918 he was awarded the Military Cross,[4] which was gazetted on 2 July. His citation read:
2nd Lieutenant Harold Vincent Tewson, West Yorkshire Regiment.
"For conspicuous gallantry and devotion to duty. When his men came under very severe machine-gun fire he dashed in front, and so encouraged them by his fearless example that they drove the enemy back and captured the objective. When the fire became so heavy that a gap was caused on his flank, he ran along the front of the line, rallied the men and formed a defensive flank, thus saving a critical situation."[5]
On 1 February 1919 Tewson was promoted to lieutenant in the 5th Battalion of the West Yorkshires.[6]
After the war, Tewson returned to Bradford to work for the Dyers Union.[1] He became involved with the Independent Labour Party, and, aged 25, became the youngest member of Bradford City Council.[2] He joined the TUC in 1925, as Organization Secretary, and was appointed Assistant General Secretary in 1931.[7]
Tewson succeeded Walter Citrine as General Secretary of the TUC in 1946,[1] 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.[1] He was knighted on 14 March 1950.[12] Tewson retired as General Secretary in 1960, and in November of that year was appointed a part-time member of the London Electricity Board.[13] In 1964 he was appointed a member of the Independent Television Authority.[14]