"He then exited the vehicle and continued fleeing south across the line as he was sacked upon by other soldiers from North Korea", the UNC said in a statement.
"A North Korean soldier defected from a guard post on the North Korean side of the JSA toward our side at 3:31 p.m.", according to a military official.
It's the same border area which was visited by US Secretary of Defense James Mattis less than a month ago.
According to the South Korean military there was no exchange of fire across the border, and the UNC statement stressed that no South Korean or United States forces were harmed.
During his trip, Trump struck a tough tone on North Korea, calling for an end to its nuclear program and saying "we hope to God we never have to use" the military strength the U.S. has on the Korean Peninsula.
"He crossed from a North Korea post towards our [South Korean] Freedom House", the South said in a statement.
North Korean leader Kim Jong Un gives field guidance to the Kumsong Tractor Factory in this undated picture provided by KCNA in Pyongyang on Wednesday.
While on average more than 1,000 North Koreans defect to South Korea every year, most travel via China and it is unusual for a North Korean to cross the land border with South Korea.
Meanwhile, three US aircraft carriers are joining a combined exercise with the South Korean Navy in the East Sea in a show of force against North Korea.
The four-day simulated exercises, which will go on until Tuesday, 14 November, will include participation from South Korean naval forces as well.
The man made it 50 yards over the dividing line and took cover behind a building on the southern side of the line that separates the two Koreas.
From there they can seek sanctuary and organise a flight to South Korea, where defectors are given assistance and prepared for life outside the hermit state.
He didn't elaborate on what "the last" might be, but North Korea has launched ballistic missiles that have the potential to strike the USA mainland, and it recently conducted its largest-ever underground nuclear explosion.
The incident left three North Korean soldiers and one South Korean soldier dead.
The defection came during escalated tensions between the North and the South and almost a week after President Trump visited Seoul for his five-country Asia tour.
Although there have been a handful of defections across the DMZ in recent years, escapes through the tense Joint Security Area are rare. The attack prompted Washington to fly nuclear-capable B-52 bombers toward the DMZ in an attempt to intimidate North Korea.