She is now the first royal family member to run for office since absolute monarchy was overthrown in a 1932 coup.
Pheu Thai is also fielding candidates in the election, and Thai Raksa Chart was formed by Thaksin loyalists and the core leadership of the United Front for Democracy Against Dictatorship (UDD), or "red shirts" group, as a strategy to help Pheu Thai win seats, or to act as a back-up if the main party was disqualified.
In an online post titled "Thank you", the former royalty said she is exercising her political rights as a commoner by contending atop Thai Raksa Chart Party's ticket.
She has cast her lot with a party affiliated to former prime minister Thaksin Shinawatra, who was deposed by the army in a 2006 coup.
Ubolratana's nomination has electrified the buildup to a March 24 election which had seemed poised to return the junta and its proxies to power in some form.
The royal family is highly regarded in Thailand and carries great influence - especially in the case of recently deceased and longstanding King Bhumibol Adulyadej.
"The (party) board agrees that the name of Princess Ubolratana, an educated and skilled person, is the most suitable choice", Thai Raksa Chart party leader Preechapol Pongpanich told reporters.
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.
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"Their supporters and the supporters of the elite have clashed many times over the past decade, so to now come to this stage to have a member of the royal family running to be potentially the prime minister for a party backed backed by the Shinawatras is definitely an intriguing development for Thai politics".
"I have thoroughly considered the party's policies and I deem that they can further the programmes the [military regime] has initiated.so I accept the Phalang Pracharat Party's nomination as a prime minister candidate", Prayut said in a statement. "I want to reassure that I do not intend to hang on to power". It is not clear what the king thinks about his sister's entry into politics.
The Princess' candidacy would only become official after the EC verifies her eligibility to stand for PM, Preechaphol said. She received her Bachelor of Science from MIT and went on to receive her Masters in public health at the University of California.
Beyond her royal appearances at charities and events, Princess Ubolratana is an avid social media user who has close to 100,000 followers on her personal Instagram page.
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.
Her son was killed in the Indian Ocean tsunami in 2004.