He served with the army in North Africa and Italy during the war. Arthur married Marjorie in 1948, and continued to be involved with the Liberal Party. He was chairman of its committee on the elderly from 1948 to 1949. Seldon was working at the Brewer's Society in 1956 when approached by Lord Grantchester to be asked if he wanted to join a new 'Think Tank' just set up by Antony Fisher on the advice of Friedrich Hayek, founder of the Chicago School of economics and champion of free market neoliberalism. Seldon wrote a first pamphlet still only 20 years of age, called "The Intellectuals and Socialism" (1937) in which he criticised the Keynesian state and its bureaucracy as "second hand dealers in ideas." Ralph Harris was appointed General Director of the new Institute of Economic Affairs and Arthur was Editorial Adviser. Antony, later Lord Fisher left a legacy of think tanks that he had founded all around the world. "The State Versus Market" pamphlet was published when he was still only twenty years old, based on a book review, it explained the benefits of market competition. Seldon joined the Liberal Party. He was on a Committee of Enquiry chaired by Elliott Dodds into the distribution of property, exploring the idea of "ownership for all," and the effects of statist maldistribution. In "The Drift to Corporate State" he severely criticised the corporatist industrial policy being against state monopoly. It was an idea endorsed by the Liberal Assembly ten years earlier in 1948. In another pamphlet in 1957, the IEA published "Pensions in a Free Society" commented freely on the Liberal Beveridge Report of 1942 into founding of the state pension system. Seldon generated editorial copy: edited recruited authors, made available titles to a wider audience. Pamphlets were of between 10,000 and 15,000 words and as such represented a new form of political literature. It was also Seldon's inspiration to produce series, such as Hobart Papers, Occasional Papers, and Readings etc. Seldon was also involved in the famous Orpington by-election in 1962, in which the Liberal Party gained the seat from the Conservative Party and weakened the confidence of the Macmillan administration. A neoliberal free marketeer, he influenced the policies of Margaret Thatcher. In 1970 Seldon invited Milton Friedman at the IEA, quick to recognise the value of monetarist policy. The ideas imported from Chicago had a great influence on members