The White House announced the nomination Tuesday morning, Thailand time. Before it becomes official, the Senate must approve Mr Davies' appointment, which comes amid strains in the US-Thai alliance.
Washington suspended military aid to Thailand in response to the May 22 coup.
Mr Davies served as the Obama administration's point man for the diplomatic response to North Korea's nuclear programme between 2012 and 2014. Prior to that, he was the US representative to the International Atomic Energy Agency in Vienna.
The previous US ambassador to Thailand, Kristie Kenney, left the post in November.