Manoon graduated from the Chulachomklao Royal Military Academy in Class 7, along with classmates Sanan Kachornprasart, Chamlong Srimuang, and Pallop Pinmanee.

[1] The Young Turks were increasingly frustrated by the military leadership, which they claim had "allowed themselves to be subservient to the rotten political system just to live happily with benefits handed to them by (corrupt) politicians.

[1] The Thai royal family immediately fled to Nakhon Ratchasima Province, along with Prime Minister Prem Tinsulanonda.

[7] Senate Speaker Manoonkrit, citing a petition signed by some 60,000 people, forwarded a formal request to the National Counter Corruption Commission (NCCC) to investigate four Constitutional Court of Thailand judges: Kramol Thongdharmachart, Phan Chanpan, Sak Techacharn, and Jumpol na Songkhla in connection with their rulings on the asset concealment case against Prime Minister Thaksin Shinawatra, which then triggered major legal questions and a constitutional paradox.

President Uthai Pimchaichon, who was also speaker of the House of Representatives, asked the Constitutional Court to block the investigation launched by the NCCC.

"[10] On 20 May 2003, Manoonkrit announced his resignation from the posts of Senator and Speaker effective on 4 January 2004, after some members of the upper house tried to force him to step down following a debate calling for an evaluation of his performance.