The announcement comes just one week after North Korea launched four ballistic missiles into the sea off Japan.
The US Army is permanently stationing an attack drone system and its support personnel in South Korea amid ongoing tensions with the North, a Department of Defense spokesperson said.
Officials said the deployment, due by next year, was not unique to South Korea, and was being conducted across the Army to provide infantry divisions with better intelligence.
But the announcement comes just one week after Pyongyang launched four ballistic missiles in its latest provocative test.
"The US Army, after coordination with the Republic of Korea Armed Forces and the US Air Force, has begun the process to permanently station a Gray Eagle Unmanned Aerial Systems company at Kunsan Air Base, Republic of Korea," Pentagon spokesman Navy Captain Jeff Davis said on Monday.
The sensor-rich MQ-1C Gray Eagle is capable of carrying Stinger and Hellfire missiles, as well as other armaments.
It "adds intelligence, surveillance and reconnaissance capability to that particular infantry division, as well as to our Korean allies," Davis said.
North Korea fired at least four missiles toward Japan last week — three of which splashed down in waters near Japan — saying they were tests for a possible strike on US bases in Japan.
A US missile defence system, THAAD, is being deployed to South Korea in the face of threats from the North.
The US has about 50,000 troops in Japan, and another 28,000 in South Korea.