Bush and the first lady will spend August 6 and 7 as guests of the Thai government, Tharit Charungvat told reporters.
"He will deliver a speech about the US position toward Asia," he said.
Bush, whose term ends early next year, will also meet Prime Minister Samak Sundaravej, Tharit added.
The White House website said the purpose of the trip was "to celebrate 175 years of the US-Thailand relationship and to discuss issues bilateral and regional issues with Prime Minister Samak."
Bush is scheduled to be in South Korea before heading to Thailand.