[2] In 1933 Marshall entered Downing College, Cambridge as an exhibitor, supported by scholarships from both the Cambridgeshire County Council and the Board of Education.
However, Gardiner advised Freddy to broaden his horizons and introduced him to a Commander Hawkridge who had an office insuring fishing boats in Hull.
These trips may have had some influence on Marshall's decision to give up embryology and to apply for a post as a marine biologist in Hull.
[2] Marshall was appointed to be part of Alister Hardy's Department of Zoology and Oceanography at University College, Hull in 1937.
[2] Marshall was commissioned in to the Royal Army Ordnance Corps in 1941 and stationed on the Thames for a while before being transferred, like many other biologists, into operation research.
He returned to Liverpool on board a Free French cargo ship, the Indochinois accompanied by Surgeon Commander Edward W. Bingham, who had much more experience with huskies than Marshall.
On arrival at Liverpool they and the dogs were transferred to the RSS John Biscoe to sail to the Antarctic, where he was based at Hope Bay as the zoologist.
He also conducted a well received series of lectures at Harvard University and worked at the Woods Hole Oceanographic Institution in 1963.
In 1972, Marshall left his position at the museum to become the Chair of Zoology at Queen Mary College, London University and remained in that post until he retired in 1977.
In 1996 Marshall and Olga moved to Great Chesterford in Essex where he died suddenly on 13 February 1996 while working on a new book about simplicity in biology.