Chŏng Mong-ju was born in Yeongcheon, Gyeongsang Province to a family from the Yeonil Jeong clan (연일 정씨; 延日 鄭氏).

[1] In 1367, he became an instructor of Neo-Confucianism at the Gukjagam, then called Songgyungwan, whilst simultaneously holding a government position, and was a faithful public servant to King U.

Around this time, because the Waegu (왜구; 倭寇 - the Japanese pirates) invasions of the Korean Peninsula were extreme, in 1377 Chŏng Mong-ju was dispatched as a delegate to Kyūshū in Japan.

At this time, the tandai of Kyūshū, Imagawa Sadayo, made several repressions against the Waegu, probably as a direct result of Chŏng Mong-ju's diplomacy.

Chŏng Mong-ju's noble death symbolizes his faithful allegiance to the king and Goryeo, and later he was venerated even by Joseon monarchs.

Chŏng Mong-ju's murderer, Yi Pang-wŏn (later Taejong of Joseon), inscribed the words "Defender of Goryeo" on his tombstone to praise his loyalty.

The diagram ( — ) represents Chŏng Mong-ju's unerring loyalty to his king and his country towards the end of the Goryeo Dynasty.

이몸이 죽고 죽어 일백 번 고쳐 죽어                此身死了死了一百番更死了。      (차신사료사료일백번갱사료) 백골이 진토되어 넋이라도 있고 없고              白骨爲塵土魂魄有也無。              (백골위진토혼백유무야) 임 향한 일편 단심이야 가실 줄이 있으랴         向主一片丹心寧有改理也歟。      (향주일편단심유개리여) Though I die and die again a hundred times, That my bones turn to dust, whether my soul remains or not, Ever loyal to my Lord, how can this red heart ever fade away?