The general election for Thais to elect members of parliament will be held on March 24, the first since the 2014 coup during which the National Council for Peace and Order came into power.
The party officially registered the elder sister of His Majesty King Maha Vajiralongkorn as news people pushed for vantage points at the Office of the Election Commission.
Party leader Preechaphol Pongpanit said that everything was in accordance with the Constitution - the fact that an immediate member of the royal family was now Thai Raksa Chart's candidate for Prime Minister would not give it any advantage over its rivals, he said.
"The party has nominated the princess as its sole candidate", Thai Raksa Chart Party leader Preechapol Pongpanich told reporters after registering his party's candidate at the Election Commission.
Although her father's favorite, she was virtually disowned by him in 1972 when she married an American who was a fellow student at the Massachusetts Institute of Technology.
It also pits her against the preferred candidate of the military, which is considered one of Thailand's most royalist institutions.
Thailand has not had a royal as premier since becoming a constitutional monarchy in 1932.
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In general, like most of the royal family, she publicly kept herself aloof from Thailand's recent political turmoil.
Her relationship with her brother, King Vajiralongkorn, is less clear.
The conflict between the Bangkok-centered, royalist elites and Thaksin and his more rural-based supporters has resulted in street protests, military coups, and violent clashes over nearly 15 years. However, the death in 2016 of King Bhumibol Adulyadej added a major element of uncertainty, as he had served as a stabilizing force since taking the throne in 1946.
"She is knowledgeable and is highly suitable".
Following her divorce, she returned to Thailand and has once again begun to participate in royal life although she never took up her full royal title.
But the pro-Thaksin side was always likely to win the largest share of the seats; with a royal candidate for prime minister it has an additional, significant advantage, given the nearly instinctive reverence for royalty among many Thais.
Soon after Friday's announcement, her catchphrase #SongPhraSlender (Long Live Slender) was number one on Twitter in Thailand.