Kim ultimately edged out Cho in a three-hole play-off at Woojeong Hills Country Club in Cheonan, after the two players had each finished regulation play on four-under-par.
Jarin Todd and Hyungjoon Lee were each one shot behind, with the latter suffering heartbreak on the 72nd hole as he carded a double-bogey seven to drop from first to joint third and miss out on both his national title and qualification for The Open.
Both Kim and Cho will be making their maiden major championship appearances at St Andrews.
Kim, 21, became the youngest winner in Challenge Tour history when he won the 2018 D+D Real Czech Challenge at the age of 17 and he now has his first win on home soil.
He was the star performer in the final round, shooting a two-under 69 – the equal-lowest score of the day – to climb to the top of the leaderboard. Although Kim bogeyed the last, he had still done enough to earn a share of first place. A seven-foot putt on his return to 18 then sealed victory in the play-off.
“It’s such a great honour,” said Kim when asked about his qualification for The 150th Open.
“I’ve grown up watching The Open as a kid and I just can’t express how happy I am. Everyone talks about St Andrews. It’s such a historic golf course and I just can’t wait to be there.”
Cho’s wait for his first professional title in Korea continues, but the 33-year-old – a two-time winner on the Japan Golf Tour – can nevertheless also celebrate an upcoming trip to the home of golf.
“I think it was 1998 when Justin Rose first played The Open as an amateur, that was the first time I learned about the Championship,” said the 33-year-old.
“Playing in a major has always been my goal ever since and it’s a great honour to finally have the opportunity. It’s my first time travelling to the UK for any golf championship. I’m really looking forward to the event.”
The joint overnight leader after a superb 67 on Saturday, Cho closed with a one-over 72 to match Kim’s 72-hole total. Taehoon Ok, who had been level with Cho after 54 holes, could only muster a four-over 75 and slipped back into a tie for sixth.
The KOLON Korea Open was the latest event in The Open Qualifying Series, which provides golfers with opportunities to reach St Andrews at events around the world on the PGA TOUR, DP World Tour, PGA Tour of Australasia, Asian Tour, Korean Tour, Japan Golf Tour and Sunshine Tour.
Sixteen more players will book spots in The 150th Open when Final Qualifying takes place on Tuesday, before The Open Qualifying Series concludes with the Horizon Irish Open, John Deere Classic, Genesis Scottish Open and Barbsaol Championship.