An orphan, on leaving school in 1796 he was apprenticed to a South Sea whaler. In his second year on her she was wrecked in the Pacific, and her crew was picked up by an American ship. The captain called in at the island of Massa Feura to collect water, and, apparently as a joke, marooned Thomas and a friend there. The friend died, and Thomas killed and cured seals until he was picked up by another American ship. He bought a passage back to England with half of his 5000 sealskins. Almost home, he was pressganged, but was eventually appointed ship’s schoolmaster and taught the midshipmen surveying. He became a pilot in a military attack on Walcheren, and was rewarded for his skill by receiving the rank of surveyor, and sent to supervise the building of the survey ship Investigator. Thomas became her master. In 1817 he took the survey to Shetland, and spent 20 years – far more than his employers had envisaged - preparing a chart of the islands. A Shetland friend remarked later: 'He was thorough enough to give us soundings of the Loch of Cliff, "in case", as he put it, "there might be a canal cut to the sea". He started to mark down peat-stacks on his chart, until he was laughed out of the absurdity by consumers of the fuel.' His Shetland chart appeared in 1838, and he went on to survey Orkney. His son Frederick William Leopold Thomas accompanied him from 1828, aged 13, and later succeeded him in the Orkney survey. George Thomas also prepared sailing directions for Orkney and Shetland, published in the North Sea Pilot in 1857. He died in Autumn 1846.