The Democrat Party (Thai: พรรคประชาธิปัตย์, RTGS: Phak Prachathipat, pronounced [pʰák prà.t͡ɕʰāː.tʰí.pàt]) is a conservative-liberal Thai political party. The party is the oldest active political party in Thailand, it was founded in 1946 as a royalist party; it now upholds a right-liberal and pro-market position.

The Democrat Party made its best showings in parliament in 1948, 1976, and 1996. It has never won an outright parliamentary majority. The party's electoral support bases are southern Thailand and Bangkok, although the party's strength in Bangkok has declined rapidly since the 2019 general election. Since 2004, Democrat candidates won three elections for the governorship of Bangkok. From 2005 to 2019 and since 2025, the Democrat Party has been led by Abhisit Vejjajiva, former prime minister.

The Thai name of the party, Prachathipat (ประชาธิปัตย์), is derived from the word prachathipatai (ประชาธิปไตย) which means 'democracy', 'democratic' or 'democrat'. The party said it wanted the term to mean the people in whom democracy is vested.

The Democrat Party was founded by Khuang Aphaiwong on 5 April 1946, but the party considers 6 April as the party's founding day, to coincide with Chakri Memorial Day, as a conservative and royalist party, following the January 1946 elections. Early members included royalists opposed to Pridi Phanomyong and former Seri Thai underground resistance members. The party competed against the parties affiliated with Pridi Phanomyong and the Progressive Party of brothers Seni and Kukrit Pramoj. In the January 1946 elections, the Pridi-led coalition had won a majority in parliament. However, Pridi declined the nomination as prime minister and the parliament appointed Khuang as premier. Khuang resigned in March 1946, after being defeated on a bill, and was replaced by Pridi. The smaller Progress Party later merged with the Democrat Party.

After the death of King Ananda Mahidol in 1946, the Democrat Party accused Pridi of having been the mastermind behind the king's death and spread this propaganda throughout the capital. Seni Pramoj's wife told the US chargé d'affaires that Pridi had the king assassinated, and Democrat Party members spread the same rumor to the British Embassy. A few days after the king's death, a Democrat MP yelled out, "Pridi killed the King!" in the middle of a crowded theater.

By the time of the elections of August 1946, the Democrat Party was backed by royalists like Prince Upalisarn Jubala, Srivisarn Vacha, Sridhamadibes, Borirak Vejjakarn, and Srisena Sombatsiri. Except for Prince Upalisarn Jubala, all of these figures would become Privy Councilors to King Bhumibol Adulyadej. Parties affiliated with Pridi continued to win a majority of seats in parliament. Pridi was appointed premier, but later conceded to Luang Thamrong Navasavat. A military coup led by Marshal Plaek Phibunsongkhram later overthrew the Thamrong government.

The palace persuaded Marshal Plaek to appoint Khuang Aphaiwong as figurehead civilian prime minister. In subsequent elections on 29 January 1948, the Democrats won a majority for the first time, and reappointed Khuang as premier. Khuang packed his cabinet with palace allies, much to the consternation of the military. The military later, claiming that they were supporters of constitutional monarchy, demanded that Khuang resign. Marshal Plaek replaced Khuang as prime minister.

Although having no representatives in the cabinet, the Democrats had key representatives in the constitution drafting committee. Headed by Seni Pramoj and dominated by royalists under the direction of Prince Rangsit and Prince Dhani, the 1949 Constitution elevated the throne to its most powerful position since the 1932 overthrow of the absolute monarchy. Among its features was a senate whose members were to be appointed directly by the king. The constitution triggered protests among much of the public. It was attacked as contrary to the purpose of the 1932 revolution. Critics were branded republicans and communists.