He was born in Newton Abbot, England, the son of a solicitor. He attended Westminster School until 1866 when the family emigrated to Australiasettling in Rockhampton, Queensland. D'Arcy continued his studies and chose to follow law, later joining his father's business. He did well and began to speculate, initially in land. In 1872 he married Elena Birkbeck of Rockhampton.
In 1882 he became a partner, with two other businessmen, in a syndicate with Thomas, Frederick and Edwin Morgan when they opened a mine on Ironstone Mountain (later renamed Mount Morgan). In October 1886 the syndicate became the Mount Morgan Gold Mining Company, with D'Arcy a director and the largest shareholder. In 1889, with a substantial fortune, he and his family moved to England. He bought Stanmore Hall, Bylaugh Park and a house on Grosvenor Square. His wife Elena died in 1897 and in 1899 he married Nina Boucicault, also of Rockhampton.
In 1900 he agreed to fund a search for oil and minerals in Persia headed by Wolff, Kitabgi and Cotte. Negotiations with the Shah began in 1901 and with the offer of £10,000 a sixty year concession to explore for oil was secured in May covering 480,000 miles². A drilling team under George B. Reynolds was sent to Persia and began to search. In 1903 a company was formed and D'Arcy had to spend over £500,000 to cover the costs. False hopes were raised in 1904 and D'Arcy was forced to find further financial support, with the Burmah Oil Company agreeing to put up to £100,000 into the venture in return for much of the stock.
Drilling in southern Persia at Shardin continued until 1907 when the search was switched to Masjid-I-Sulaiman (Maidan-i-Naftun). Drilling began at one site in January 1908 and at another nearby in March. By April with no success the venture was close to collapse and D'Arcy almost bankrupt, but on May 16 there were encouraging signs and on May 26 at 1180 feet they struck oil.
In April 1909 the Anglo-Persian Oil Company (APOC) was founded and D'Arcy was made a director, the company would later become British Petroleum. By 1911 APOC had run a pipeline from the find to a refinery at Abadan. In 1912 the Mount Morgan company was listed in London and D'Arcy was made chairman of that board.