Gilbert joined Ludwig Leichhardt's expedition in September 1844 which was going to cross Australia's north, from Brisbane to Port Essington. Gilbert, with his experience in the Australian bush, was unofficially the second in charge. The journey was much slower than planned and food supplies were getting low. On 28 June 1845, near the Gulf of Carpentaria, Gilbert was killed when aborigines attacked the explorers. He was buried at the site, but the grave has never been found. The rest of the group reached Port Essington in December 1845.