In an Instagram post on Saturday, the princess did not directly mention her brother or her political hopes, but thanked supporters for their "love and kindness towards each other over the past day" and expressed gratitude for their support for her.
Born in 1951, Princess Ubolratana Rajakanya Sirivadhana Barnavadi is the oldest child of Thailand's beloved late King Bhumibol Adulyadej.
She attended the Massachusetts Institute of Technology and after marrying an American in 1972, she gave up her royal title. After her divorce she returned to Thailand in 2001 and once again started participating in royal life.
The princess engages actively in social media and has also starred in several Thai movies.
Princess Ubolratana: Thai royal to stand as PM candidate (via BBC)
Ms Ubolratana is one of the more colourful members of the royal family. She has starred in movies, sung on stage with a top Thai pop group, and is flamboyantly fashionable. She portrays herself as more down-to-earth and accessible than other royals.
She was known to be a favourite of her father, the late King Bhumibol, with whom she used to sail in the Gulf of Thailand.
She began her show business career in 2003, starring in a TV drama, and going on to act in several other movies. Last year she was filmed dancing and singing on stage with the popular Thai girl band BNK48.
She also supports a number of charities, in particular one she founded called To Be Number One, which aims to help young people escape drug addiction.
Princess Ubolratana: The royal upending Thai politics (via BBC)
King Vajiralongkorn says the princess retains her status as a member of the royal family (via BBC)
Broadcast on all Thai TV networks, the statement said: "Even though she has relinquished her royal titles in writing, she maintained her status and carried herself as a member of the Chakri dynasty.
"Involvement of a high-ranking member of the royal family in politics, in whatever way, is considered an act that defies the nation's traditions, customs and culture, and therefore is considered extremely inappropriate."
Thailand party accepts king's opposition to Princess Ubolratana PM bid (via BBC)