Born 27 June 1842, in London, Henry Marc was the second son of Isambard Kingdom Brunel. He claimed to have been drawing on section paper from the age of seven, and showed an early aptitude for engineering. He was taught at Harrow School and attended the launches of the Great Eastern before being taught by M. Franzoni of Geneva for two months prior to Brunel's visit to Egypt in 1859. From 1859-1861 he was educated at King's College, London, while visiting engineers and factories. He also visited the Great Eastern at Liverpool and voyaged to America on her. In September of 1861 he became an apprentice with Sir W.G. Armstrong & Co., where he remained for two years, leaving the company to become apprenticed to Sir John Hawkshaw, whom he was the pupil of for a further three years. He drew plans and assisted with various Indian railways and the Charing Cross and Metropolitan lines, and attended trial firings of the 600 pound Armstrong Naval Gun against an ironclad target ship. Throughout 1865, he worked on marsh drainage, the Eastern Bengal Railway, and helping his brother Isambard Brunel write a biography of their father (Life of Isambard Kingdom Brunel, published by Longmans, Green & Co., 1870), providing technical expertise and insight. He also took up amateur acting, and remained a keen enthusiast for the rest of his life. In 1866 he became involved with the planning and preliminary stages of construction for the Channel Tunnel, and took soundings in the English Channel as well as borings on private land. To help with his work he took up the study of geology and studied the workings of tunneling machines cutting chalk and coal. He also worked on various projects, including the Great Eastern, the Amsterdam to North Sea Ship Canal and the West and East India Docks. In 1869 he worked on an experimental new atmospheric railway system for use on the Oxford Street Railway line. He then worked on various civil projects, including sewers in Brighton, the Albert Dock at Hull and Dover Harbour. By 1870 his work on writing the life of Isambard Kingdom Brunel had begun to eat away at his other commitments, forcing him to resign from Hawkshaw's employ and prohibiting him from leaving England. In 1871 he set up his own practice as a Civil Engineer at Duke Street, London. He began work on rail and civic drainage contracts for Torquay, drawing up parliamentary plans for the Torquay Railway and levelling land for the Birmingham city sewers. Work continued on the prospective Channel Tunnel, as well as rail work and drainage throughout England. In 1876 he was elected to membership of the Athenaeum Club, and in 1878 he went into partnership with John Wolfe Barry. From 1880 he was a member of a company designed to promote Tower's Spherical Engine, and continued work on the Torquay reservoir. In 1882 he began work on an experimental rowing boat designed to be rowed while facing forward. Throughout 1886 he was involved with Beauchamp Tower in working on Tower Bridge, London, as well as continuing in his experiments in "rumming" (rowing forwards). He worked on many projects including an electric hearing aid, ship's log, gyroscope for naval instruments and military rangefinder in addition to his projects in civil engineering and naval architecture.
He was a member of the Institute of Civil Engineers and an associate member of the Institute of Naval Architects, as well as Scientific and Amateur Dramatic Societies.