Walter Garstang FLS FZS (9 February 1868 – 23 February 1949), a Fellow of Lincoln College, Oxford and Professor of Zoology at the University of Leeds, was one of the first to study the functional biology of marine invertebrate larvae. His best known works on marine larvae were his poems published as Larval Forms and Other Zoological Verses, especially The Ballad of the Veliger. They describe the form and function of several marine larvae as well as illustrating some controversies in evolutionary biology of the time.

Garstang was known for his vehement opposition to Ernst Haeckel's Biogenetic Law, now discredited. He is also noted for his hypothesis on chordate evolution, known as Garstang's theory, which suggests an alternative route for chordate evolution from echinoderms. The last-cited reference gives special attention to how the ideas of Garstang's predecessors profoundly influenced his biological theories.

Walter Garstang was born on 9 February 1868 as the eldest son of Dr Walter Garstang of Blackburn and his wife Matilda Mary Wardley, and older brother of the archaeologist John Garstang.

In 1895, he married Lucy Ackroyd; they had one son, Walter Lucian Garstang,. and five daughters.

In 1884, at the age of 16, he was awarded a scholarship to Jesus College, Oxford and was initially going to study medicine. Under the guidance of Henry Nottidge Moseley, he shifted to and joined the school of Zoology and graduated in 1888 at the age of 20. Before graduation, Garstang was offered a position as secretary and assistant to Gilbert C Bourne, the new resident director of the Marine Biological Association of the United Kingdom in Plymouth. There he met Ray Lankester. In 1891, he left Plymouth and was a Berkley Research Fellow under Milnes Marshall at Owens College, Manchester. A year later, Garstang returned to Plymouth as Assistant Naturalist, only to be elected a Fellow of Lincoln College, Oxford, in 1893. In 1894, while Ray Lankester held the Linacre Chair, he became a lecturer at Lincoln College and in 1895 he started the series of Easter classes in which he took students on week-long field courses to Plymouth.

Between 1902 and 1907, Garstang was employed by the MBA as the principal investigator working on North Sea fisheries. He helped to establish a fisheries laboratory in Lowestoft that was later to become the Centre for Environment, Fisheries and Aquaculture Science (Cefas), part of the Ministry of Agriculture, Fisheries and Food (United Kingdom). Garstang instigated a series of detailed fisheries surveys throughout the southern North Sea aboard the RV Huxley, under the auspices of the newly formed International Council for the Exploration of the Sea (ICES).

Garstang was Professor of Zoology at the University of Leeds from 1907 to 1933. The Garstang Building at the university is named in his honour. In 1912, in cooperation with Professor Alfred Denny of the University of Sheffield he established the Robin Hood's Bay Marine Laboratory. The minutes of Sheffield's Faculty of Pure Science on 12 March 1912 record the following resolution that was carried unanimously: That the Faculty approves of the proposal to extend the work of the Department of Zoology by co-operating with the University of Leeds in establishing a small marine Zoological Laboratory at Robin Hood's Bay.

In his time, Haeckel's biogenic law was being replaced, but biologists were not sure what exactly should replace it. Some preferred to discard it completely, so that development and evolution are not related. Garstang preferred to modify it.