As early as 1804 Redfern began advocating for the use of a new smallpox vaccination. After an examination of his level of medical knowledge by the Surgeon-General of New South Wales, Thomas Jamison, it was certified that Redfern was "qualified to exercise the profession of a surgeon, etc." In 1808 he returned to Sydney and was appointed by Governor Joseph Foveaux to the role of assistant surgeon for the new Sydney Hospital. Foveaux planned to confirm Redfern's appointment and stated that his "skill and ability in his profession are unquestionable, and his conduct has been such as to deserve particular approbation".