In December of the same year, he transferred to Virtuous Law School (의법학교; 懿法學校), from which he graduated on July 9, 1909, and immediately entered its advanced program (고등과) in the following September.

Subsequently, in January 1911, he enrolled at the Private Youth Academy (사립청년학원; 私立靑年學院) in Sangdong (상동), southern Seoul, where he received Hangul instruction from his lifelong mentor, Si-gyeong Ju.

[3] In the spring of 1913, after graduating from the Private Youth Academy, Kim began teaching Korean, history, and mathematics in the advanced program at Changsin School (창신학교; 昌信學校) in Masan.

[3][4][5] He lectured there for four years, during which he authored his early scholarly work, a paper titled The Basis of Joseon Language Research (조선어 연구의 기초).

[4] By January 1922, Kim drafted a paper titled On Correcting Our Language and Script by Observing Their Past and Present Forms (우리말과 글의 예와 이제를 보아 바로잡을 것을 말함).

[2][4] Kim graduated from Yonhi College on March 24, 1922, and taught Korean and history at Paiwha Girls' General High School (배화여자고등보통학교; 培花女子高等普通學校) until 1926.

[2][3][4][5] He completed his thesis, A Historical Examination of Joseon Script (조선 문자의 역사적 고찰), on September 17, 1928,[3][4] and earned a bachelor's degree in East Asian history in 1929 at the age of 36.

After graduating from Rikkyo University, Kim returned to teach at Paiwha Girls' General High School[2][3][4][5] and was actively involved in the Joseon Language Research Institute.

[4] As the Japanese fascist regime intensified, Kim suffered significantly due to the Self-Cultivation Friendship Association incident (수양동우회사건; 修養同友會事件) in 1937.

[3][4] He was acquitted by the high court in October 1941[4] and began working as a teacher at Sungshin Girls' School of Home Economics (성신가정여학교; 誠信家政女學校) in April 1942.

He passed away at Busan First Hospital, and his funeral, held as a public ceremony,[3][4] took place on February 9 in Gwangjiwon-ri, Jungbu-myeon , Gwangju County, Gyeonggi Province.

[4] After being reinstated as a teacher at Paiwha Girls' General High School, he was appointed to the editorial committee for the Joseon Language Dictionary (조선어사전) to systematically organize the accumulated results of Hangul research.

Compiled as a textbook for middle and high school students, this work is the final grammar book to be published, written from a structuralist and analytical linguistic perspective.

It further classifies Saenggak-ssi into nouns, adjectives, and verbs, To-ssi into postpositions, conjunctions, and sentence-ending particles, and Moeim-ssi into determiners, adverbs, and interjections, which results in nine parts of speech in total.

[15] Boh-yuong Shin, a professor of Political Science at Konkuk University, argues that this assessment has led to Choe being unfairly maligned as a historical sinner.

Shin emphasized that while Man-ri Choe regarded the invention of Hangul as a significant accomplishment, he also expressed several concerns about its implications and worried about its adverse effects on King Sejong's health.

[14] In an interview published in the Kyunghyang Shinmun on December 20, 1965, Kim Yun-kyong remarked, "Initially, it felt unfamiliar and awkward, but the successful replacement of 'bento (べんとう)' with 'dosirak (도시락)', 'donburi (どんぶり)' with 'deopbap' (덮밥), and 'yakiniku (やきにく)' with 'bulgogi (불고기)' serves as an excellent example.

Drawing from Kim's interview, Kyo-ik Hwang – a former journalist now a blogger and YouTuber – mentioned on a TV program and his Facebook page in 2018 that 'bulgogi' is a Korean adaptation of the Japanese word 'yakiniku'.