The White House announced the nomination Monday. The Senate has to approve Davies' appointment, which comes amid strains in the U.S.-Thai alliance.
Washington suspended military aid to Thailand in response to a coup against an elected government last May. The military-dominated government has cracked down on dissent and political opponents, and it remains unclear when civilian rule will be restored.
Davies served as the Obama administration's point man for the diplomatic response to North Korea's nuclear program between 2012 and 2014. Prior to that, he was the U.S. representative to the International Atomic Energy Agency in Vienna.
The previous U.S. ambassador to Thailand, Kristie Kenney, vacated the post in November.