Du Cros is the third of seven sons of Harvey du Cros. He is brought up in modest circumstances. His father, later a well-known manufacturer, is at the time only a bookkeeper with an income of £170 a year. He attends a national school in Dublin and then enters the civil service at the lowest grade. In 1892 he joins the Pneumatic Tyre and Booth’s Cycle Agency Ltd, of which his father is now the chairman, and is made a joint managing director in 1896 when it is floated as a public company.
In 1895 du Cros marries Maude Gooding, the daughter of a Coventry watch manufacturer. They have two sons and two daughters before a divorce in 1923.
In 1901 du Cros founds the Dunlop Rubber Company, converting 400 acres of land in Birmingham to produce and manufacture tires, with the area henceforth being known as Fort Dunlop. The firm eventually diversifies into making other rubber products as well as tires, and du Cros selects plantations in Malaya and Sri Lanka for the company, which by 1917 owns 60,000 acres of rubber-producing land.
In 1906 du Cros enters politics, unsuccessfully contesting the seat of Bow & Bromley as a Conservative Party candidate, a seat his brother is elected to in 1910. In 1908 he is elected Member of Parliament for Hastings, a position his father had held immediately before.
In 1909 du Cros forms, and is director of, the Parliamentary Aerial Defence Committee to ensure funding for military aeronautical development, of which he is a strong proponent. During World War I he works for the Ministry of Munitions on an honorary basis, buying two motorised ambulance convoys out of his own money and helping raise an infantry battalion, being a former captain of the Royal Warwickshires and for some years being the honorary colonel of the 8th battalion of the Royal Warwickshire Regiment. In 1916 he is created a baronet. He continues to represent Hastings until 1918, when he is elected as a Member of Parliament for Clapham, a position he resigns four years later.
His later career is awash with financial impropriety. He finds it difficult to distinguish between personal and company assets, using company funds to sponsor family investments and appointing family members to senior position with no regard for merit. He also participates in financial manipulation, being a close associate of James White, a financial expert who specialises in share rigging and whose actions leave Dunlop, had already lost influence within the company, close to collapse in 1921. He is quietly removed after the 1921 crash.