The Kenya-born Kirwa claimed the race in a time of two hours 25 minutes 37 seconds, breaking away from Japan's Ryoko Kizaki to clinch gold in Incheon.
Kizaki (2:25.50secs) was the clear silver medallist, with Kirwa's countrywoman Lishan Dula Gemechu edging Japan's Eri Hayakawa for the bronze. Gemechu (2:33.13secs) finished a second ahead of Hayakawa.
Games officials were forced to condemn Indian boxer L Sarita Devi, after the athlete refused to accept her bronze medal on Wednesday.
Sarita was beaten in the lightweight semi-finals on Tuesday, but remained distraught as she refused to wear her bronze medal around her neck on the dais.
She may not have to worry about it claiming it though, with the Olympic Council of Asia pondering taking the medal off her.
"She needs to respect the official ruling and show sportsmanship. Her actions were not sportsman-like," Incheon's organising committee deputy secretary general Son Cheon-taik said on Thursday.
"The Olympic Council of Asia is working on the review of the medal, whether or not to give it to her or confiscate it. So they are deciding what to do with it."
Chinese divers Yuan Cao and Chao He finished one-two in the men's three-metre springboard.
Cao (523.65 points) and He (503.80) were well clear of bronze medallist Sho Sakai of Japan (456.05).