During World War II Luns was posted to Switzerland, Portugal, and the United Kingdom. During 1949–1952 he represented his country at the United Nations (UN). Luns served as foreign minister from 1952 to 1971. He was a cofounder and signatory of the 1957 Treaty of Rome and, as a member of the Catholic People's Party, was elected four times to parliament. In October 1971 he was appointed secretary-general of NATO, a position he formally assumed in early 1972.
As foreign minister, Luns was convinced that strong transatlantic relations and a united Europe were not mutually exclusive. He was committed to maintaining strong ties with the United Kingdom and the United States, and he worked hard to bring Britain into the European Community as a counterbalance to Franco-German codomination in Europe.
As NATO secretary-general, Luns was a strong supporter of the United States. In 1974, under his supervision, NATO members signed the Declaration on Atlantic Relations, which reaffirmed the European–North American partnership and promoted the further development of transatlantic cooperation. Under his leadership, NATO successfully negotiated strategic nuclear weapons reductions. In 1983, NATO's European signatories decided to reduce nuclear warheads in Europe, which was eventually implemented. Multilateral and balanced force reductions were, however, less successful. In 1982 Spain was invited to join NATO, which was the first enlargement of the organization in twenty-seven years. Luns retired in June 1984 and died in Brussels on 18 July 2002.
Luns, Joseph M. A. H. The Western Alliance: Its Future and Its Implications for Asia. Singapore: Institute of Southeast Asian Studies, 1985.; Schmidt, Gustave, ed. A History of NATO: The First Fifty Years. 3 vols. New York: Palgrave Macmillan, 2001.; Stewart-Smith, Geoffrey, ed. Global Collective Security in the 1980s. Richmond, UK: Foreign Affairs Publishing, 1982.