Thomas Gilbert was an 18th-century British mariner.
Thomas Gilbert and John Marshall were the captains of two East India Company vessels, the Charlotte and the Scarborough, returning from carrying convicts to Botany Bay in 1788, when they sailed through the Gilbert Islands and described Aranuka, Kuria, Abaiang and Tarawa.
The vessels had been part of the first fleet carrying convicts to Australia. They had sailed in a convoy under the command of post-captain Arthur Phillip, New South Wales' first Governor.
The two vessels encountered their first island in the Gilberts on 17 June 1788. In a 1941 article in Life Samuel Eliot Morison wrote that this Island was probably Abemama, but might have been Aranuka. Gilbert visited Tarawa on 20 June 1788. Sketches he made survive.
The First, Second and Third Thomas Shoals in the Spratly Islands are named after Captain Thomas Gilbert. They, along with the Scarborough shoal, were discovered during the Scarborough's voyages through the South China Sea. Gilbert has living descendants thought to be in the Gulf Coast region of the United States.