Alan Grant-Dalton (sometimes identified as Dalton, Alan Grant) was educated at Marlborough College, a school in Wiltshire. In 1868 he was articled to the engineer-in-chief of the Liverpool Docks. From 1872 to 1874 he was on the staff of the Madeira and Mamori Railway Company in Brazil. He was engaged in surveying and exploring, including a canoe trip up the Madeira rapids into Bolivia.
In February 1875 Grant-Dalton came to the Cape Colony and that same month joined the staff of the Cape Government Railways. In January 1891 he was appointed resident engineer at the Midland and Eastern Junction. From July 1894 he was district engineer at East London. In May 1898 he was appointed resident engineer of the Eastern railway system, and from February the next year resident engineer of the Port Elizabeth to Avontuur railway. During the Anglo-Boer War (1899-1902), in April 1901, he became chief resident engineer at Port Elizabeth, and in November that year assistant engineer-in-chief. In July 1904 he was promoted to engineer-in-chief of the Cape Government Railway, succeeding John Brown, and settled in Rondebosch, Cape Town. He still resided there in 1913, but had resigned his position in 1910 when the Union of South Africa was formed.
Grant-Dalton was a member of the (British) Institution of Civil Engineers. He joined the Cape Society of Civil Engineers as a foundation member late in 1902 and chaired the society's first official meeting on 14 January 1903. He served as joint vice-president that year and the next, and became president for 1905, delivering his presidential address on 11 January. He served as joint vice-president again during 1906 and 1907, remained a member after the society became the South African Society of Civil Engineers in 1909, and served on its council again in 1913. In 1901 he joined the South African Philosophical Society and remained a member when it developed into the Royal Society of South Africa in 1908. In 1905 he became a member of the British Association for the Advancement of Science when that society visited South Africa to hold joint meetings with its South African counterpart.
In January 1878 Grant-Dalton married Emma Brehm of Uitenhage. One of their four sons, Alan Trevanian Grant-Dalton* became a civil engineer like his father.