| Honorific-Prefix: | Rear Admiral |
| Thawan Thamrongnawasawat | |
| Native Name Lang: | th |
| Order: | 8th |
| Office: | Prime Minister of Thailand |
| Term Start: | 23 August 1946 |
| Term End: | 8 November 1947 |
| Predecessor: | Pridi Banomyong |
| Successor: | Khuang Aphaiwong |
| Office1: | Minister of Justice |
| Term Start1: | 11 June 1946 |
| Term End1: | 8 November 1947 |
| Predecessor1: | Luang Chamnarnnitikaset |
| Successor1: | Seni Pramoj |
| Order2: | Minister of Interior |
| Term Start2: | February 1935 |
| Term End2: | December 1938 |
| Primeminister2: | Phraya Phahon |
| Predecessor2: | Pridi Banomyong |
| Successor2: | Plaek Phibunsongkhram |
| Birth Name: | Thawan |
| Birth Date: | 1901 11, df=yes |
| Birth Place: | Ayutthaya, Krung Kao, Siam (now Phra Nakhon Si Ayutthaya, Phra Nakhon Si Ayutthaya, Thailand) |
| Death Place: | Phramongkutklao Hospital, Phaya Thai, Bangkok, Thailand (now Ratchathewi, Bangkok, Thailand) |
| Party: | Khana Ratsadon |
| Signature: | Thawan Thamrongnawasawat signature.svg |
| Allegiance: | Thailand |
| Branch: | Royal Thai Navy |
| Branch Label: | Branch |
| Rank: | |
Thawan Thamrongnawasawat (also spelt Thawal Thamrongnavaswadhi or Thawal Thamrongnavasawat; Thai: ถวัลย์ ธำรงนาวาสวัสดิ์, in Thai pronounced as /tʰà.wǎn tʰam.roŋ.naː.waː.sà.wàt/; [3] [4]); 21 November 1901 – 3 December 1988), also known by his noble title as Luang Thamrongnawasawat, was the eighth Prime Minister of Thailand from 1946–1947. Before becoming a politician, he was a naval officer, holding the rank of rear admiral.
A career naval officer of Chinese ancestry, Thamrong was a leading member of the anti-Japanese Free Thai Movement resistance movement during World War II. He became Thailand's elected prime minister on 23 August 1946, replacing Pridi Banomyong. However, he was removed from office by a military coup orchestrated by Field Marshal Plaek Phibunsongkhram on 8 November 1947. Khuang Aphaiwong then assumed the post of prime minister.[5]
After King Rama VII abdicated the throne, Thamrong was appointed by the government to be the leader of a faculty of representatives to travel to invite Prince Ananda Mahidol, who was living in Switzerland with his mother and two siblings, to ascend to the throne as King Rama VIII of the Chakri dynasty.
However, due to political fluctuations, a coup eventually occurred originating from within a group of soldiers led by Phin Choonhavan on 8 November 1947, resulting in Thamrong having to leave the country and stay in Hong Kong for a period. When Thamrong later returned to Thailand he was appointed as a member of the Constitutional Drafting Assembly. After that, he lived a relatively quietly life.
Thawan Thamrongnawasawat died on 3 December 1988 at Phramongkutklao Hospital, aged 87 years, being the first and only naval officer to date who has served as prime minister.
Thawan has received the following royal decorations in the Honours System of Thailand: