Robert West Holmes was born in Hackney, London, England, on 25 September 1856, the son of Alice West and her husband, Robert Thomas Holmes, a brewer and (later) engraver. Little is known of Robert's early years, but it is thought that he was educated at private schools in London. He came to New Zealand in 1871 and was initially employed in the Government Printing Office. In March 1872 he joined the Public Works Department as a draughtsman and later became an engineering cadet.
From 1879 to 1887 Holmes was resident engineer in New Plymouth, where on 18 August 1884 he married Gertrude White. During this period he investigated routes for the proposed rail line from Taranaki to Auckland. In 1887 Holmes moved to Woodville for further railway construction. Then in 1890 he took charge of the Wellington district, which at the time included Marlborough. He also contributed to proposals for a tunnel to give access to Milford Sound.
In November 1891 Holmes was given charge of the partially constructed North Island main trunk railway. This project had long been proposed and construction had proceeded north from Wellington and south from Auckland, but there remained to be surveyed and constructed the most difficult section of the line, from north of Hunterville to south of Te Kuiti. This section required three major viaducts: across the Makohine and Mangateweka streams and the Makatote River. Although John Rochfort had surveyed much of the proposed route, difficult decisions about alignment remained; it was Holmes who discovered how the route traversing the upper Wanganui valley could be raised some 600 feet in around 16 miles to bring the track out onto the Waimarino plateau to the south.
During Holmes's time in charge of the project the Makohine viaduct was begun, but construction was adversely affected by interruption to the supply of steel from the United Kingdom. Holmes also identified and surveyed alternative routes for the line through Tongariro National Park and northward. The line could have no gradient greater than 1 in 50 while making the steep descent from the Waimarino plateau. Holmes brilliantly dealt with this constraint by designing the Raurimu spiral. This ingenious scheme used a series of tight left- and right-hand curves and one complete loop incorporating two tunnels.
Holmes was recalled to Wellington in 1899. In quick succession he became inspecting engineer (1901), superintending engineer (1906) and finally marine engineer and engineer-in-chief (1907); he held the last post until his retirement in 1920. From May to July 1920 he also served as under-secretary of the Public Works Department. His period of service in these senior positions saw the completion of some notable public engineering schemes: the North Island main trunk railway finally began a regular passenger service on 15 February 1909. Many of the engineering features of this line are of international standard, and it was a project largely carried through with New Zealand personnel. Another project saw the beginnings of hydroelectric generation on a national scale with the completion of the Lake Coleridge scheme in 1914.
Although Holmes's own experience was predominantly in railway design and construction he also argued strongly and consistently for adequate resources to improve and extend the New Zealand roading system. He was an early advocate of the use of a code of standards for engineering works of the type then being produced by the British Engineering Standards Association.
Holmes helped to lay the foundations for professional engineering in New Zealand. He himself lacked professional qualifications but was instrumental in obtaining the right of cadets to obtain two years' leave to study engineering at Canterbury College. His support helped to ensure that tertiary study progressively became established as the preferred route to professional qualification. Holmes also had a close involvement with the formation in 1914 of the New Zealand Society of Civil Engineers, and was twice elected to serve as president – the only man to have served more than one year. He contributed many papers to the society's journal and used the annual presidential address as a platform to take stock of national priorities for the country's engineering infrastructure. He saw the need for legislative measures to define and maintain professional engineering standards, although the Engineers Registration Act was not passed until 1924.
Holmes's contribution to engineering was recognised in his membership of the Institution of Civil Engineers, London, from 1897 and in his being given the Imperial Service Order in 1918. After retirement in 1920 he continued an active involvement with professional engineering in association with his younger son, John Dudley Holmes, in a consulting practice latterly based in Hamilton. He died on 8 February 1936, in Hamilton, and was buried in Wellington. His wife predeceased him in 1926; he was survived by two sons and one daughter.