He retired after 31 years in national politics and became active in the public sector, where he was a diplomat and lobbyist for several economic delegations on behalf of the government and as an advocate for United States–European Union relations and European integration.

His father, Huib Luns, was a versatile artist and a gifted educationalist who ended his career as professor of architectural drawing at the Delft University of Technology.

As a young student he positioned himself on the political right, favouring a strong authority for the state and being of the opinion that socialism, because of its idealistic ideology, had fostered the rise of fascism and nazism.

He joined the Dutch Diplomatic Service in 1938 and, after a two-year assignment at the Private Office of the Foreign Minister, was appointed as attaché in Bern (Switzerland) in 1940.

Bilateral relations with Indonesia and the Federal Republic of Germany, security policy and European integration were the most important issues during his tenure.

Luns believed that Western Europe could not survive the Cold War without American nuclear security and so he promoted strong and intensified political and military co-operation in NATO.

By 1956, however, this policy had proved ineffectual, but Luns and the Dutch government were still determined not to transfer West New Guinea to the Republic of Indonesia.

Luns shared Dutch public opinion in demanding that Germany recognise the damage it had caused during the Second World War, and so a mea culpa required.

He demanded that before any negotiations on other bilateral disputes could start, the amount of damages to be paid to Dutch war victims had to be agreed upon.

During the final stages of the negotiations on bilateral disputes between the two countries, Luns decided to come to an arrangement with his German colleague on his own accord.

Although he preferred integration of a wider group of European states he accepted the treaty and defended the supranational structure it was based on.

Initially, Luns stood alone and was afraid that Franco-German co-operation would result in anti-Atlantic and anti-American policies that harmed the interests of the West.

Two of De Gaulle's decisions stiffened the opposition: his denial of EEC membership to the United Kingdom in January 1963 and France's retreat from the integrated military structure of NATO in 1966.

Luns played a vital role in the negotiations unwinding French participation and continuing its political membership of the Alliance.

He owed this to his personal style in which duress, a high level of information, political leniency and diplomatic skills were combined with wit, gallant conversation and the understanding that diplomacy was a permanent process of negotiations in which a victory should never be celebrated too exuberantly at the cost of the loser.

The modernisation of the tactical nuclear forces by the introduction of the neutron bomb and cruise missiles caused deep divisions.

Because of the changes the 1960s and 1970s had brought to Dutch society and culture, the strongly conservative Luns decided not to return to his home country but instead settled in Brussels to spend his remaining years in retirement.

Luns visited the Tridentine Mass held by the Assumptionist priest Winand Kotte, who opposed the modernising policies of the Second Vatican Council, in St. Willibrord's Church, Utrecht in August 1971.