He was selected to join the Australasian Antarctic Expedition in 1911 as chief medical officer. Part of his role on the expedition was to study the effects of the Antarctic environment on other members of the expedition by taking regular blood samples and skin swabs. He took part in the Easter Sledging Journey with Cecil Madigan and Percy Correll, and after their return to main base remained there awaiting the return of Mawson, Xavier Mertz and Lieutenant Belgrave Ninnis. When Mawson returned, McLean treated his injuries and later treated wireless operator Sidney Jeffryes for symptoms of paranoia.McLean Nunataks are named in his honour. He arrived back in Australia in March 1914 and then travelled with Mawson to England.