The one-day drop-in comes as Washington reboots its relationship with Thailand under President Donald Trump.
The one-day drop-in comes as Washington reboots its relationship with Thailand under President Donald Trump, whose administration has enraged rights groups by cosying up to strongmen around the globe.
The Thai army's 2014 toppling of the civilian government pinched ties with Washington, who distanced itself from its oldest ally in Asia and trimmed back military aid.
But relations are on a better footing under Trump, with the US president extending an invitation to junta chief Prayut Chan-O-Cha.
The thaw also comes amid Washington's growing concerns of rival superpower China's clout in the region.
Beijing entices its smaller neighbours by offering massive investment decoupled from human rights concerns, which appeals to leaders weary of US pressure.
Thailand is a lynchpin country in China's massive trade and infrastructure 'One Belt, One Road' strategy.
A US Embassy spokesperson said Tillerson would discuss regional flashpoints such as North Korea's nuclear missile program and territorial disputes in the South China Sea.
It was not immediately clear how firmly the former oilman would push the junta government on its crackdown on political rights.
The US wants Thailand to "emerge as a strengthened democracy that respects and guarantees human rights and fundamental freedoms," said embassy spokesperson Steve Castonguay.
Earlier in the week Susan Thornton, acting US Assistant Secretary of State for East Asian Affairs, defended America's reach out to the military regime, as pragmatism appears to outweigh principle in Trump's foreign affairs agenda.
"They have a road map by which they're going to work towards a restoration of constitutional government, democratic elections," she said.
"It's time to go back and encourage them."
Tillerson's visit comes on the heels of a regional forum in Manila, where the former ExxonMobil CEO hailed a UN measure to pass tough new sanctions on North Korea over its growing nuclear arsenal.
Trump has tried to browbeat Beijing -- North Korea's ally and biggest trade partner -- into reining in the hermit state's ballistic missile programme.
The US has also turned to Southeast Asian nations to help isolate Pyongyang, though it failed to persuade the regional bloc to bar North Korea's top envoy from last week's forum.
Tillerson is also slated to pay respects to Thailand's late King Bhumibol Adulyadej, who has been lying in state at the Grand Palace since his death in October 2016.
Later he will travel to the Malaysian capital.