After being educated in London and Paris, Ernest joined the family publishing company, Benn Brothers. When John Benn was elected to the House of Commons in 1892 he ceased to be active in the family publishing business. Ernest Benn, now became managing director of Benn Brothers.
In 1921 William Wedgwood Benn introduced Ernest Benn to his friend, Victor Gollancz. On the recommendation of Wedgwood Benn, Gollancz was employed by Benn Brothers to develop the list of magazines the company published. Within six months Gollancz had convinced Ernest Benn to let him publish a series of art books. The books were a great success and during a seven year period turnover increased from £2,000 to £250,000 a year. Benn wrote in his diary that the increased company profits "reflects the greatest credit to the genius of Victor Gollancz".
Victor Gollancz also recruited novelists such as Edith Nesbit and H. G. Wells. One innovation was to employ Gerald Gould, fiction editor of the Observer, as chief manuscript reader. Gollancz realised that if he published works selected by Gould, the books would be guaranteed at least one good newspaper review. Gollancz believed that good reviews was a major factor in the selling of books. In critics liked a book published by the company, Gollancz purchased full-page adverts in national newspapers such as The Times and the Daily Herald to tell the public about the good reviews.
Although Ernest Benn believed Victor Gollancz was a "publishing genius" he was unwilling to give him full control over the company. There were also political differences between the two men. Whereas Benn had moved to the right during the 1920s, Gollancz had moved to the left and was now a strong supporter of the Labour Party. Gollancz had disapproved of the publication of Ernest Benn's own book, Confessions of a Capitalist, where he extolled the merits of laissez-faire capitalism.
In 1927 Gollancz left Benn and formed his own publishing company. Benn wrote in his diary: "Gollancz goes. His agreement expires next April and ever since last Christmas he has been discussing new terms. These have included the alteration of the name of the firm to Benn & Gollancz. The more we discussed the wider became our differences and the end of it all is that we agree to part. The partnership is an unnatural one. First is the fact that Gollancz must be boss, he is a natural leader and in his own interest he should set up for himself."
Ernest Benn's close friendship with his brother, William Wedgwood Benn also came to an end at this time. Wedgwood was now a Labour MP who favoured a socialist solution to Britain's economic problems. Ernest had also left the Liberals but was now a supporter of the Conservative Party.
After the 1926 General Strike Benn founded the Individualist Movement, an organisation that opposed increases in state expenditure.
Ernest Benn died on 17th January 1954.