In 1910, McCarthy volunteered to join the British Antarctic Expedition under Captain Robert Falcon Scott. With Scott, he made three Antarctic voyages. He served on the crew on Scott's failed 1912-13 Terra Nova Expedition which attempted to reach the South Pole. For his service with this expedition he received the Silver Polar Medal from King George V at a Buckingham Palace investiture. After failing in his attempt to get a place on another Antarctic expedition, on Endurance with Sir Ernest Shackleton for the Imperial Trans-Antarctic Expedition, he joined the Northern Exploration Company in Tromsø in Northern Norway which gave him the opportunity to work in the Arctic.