Even though Ms. Ubolratana officially relinquished her royal titles when she married an American in 1972, her formal entry into politics is likely to greatly complicate journalistic coverage of the campaign and election.
On Friday, five prominent analysts of Thai politics declined to comment about her candidacy. Several political activists who on social media had criticized her candidacy for unnecessarily muddying an already complicated political field quickly deleted their comments.
The deputy prime minister, Wissanu Krea-ngam, told reporters on Friday that he had no comment on Ms. Ubolratana’s candidacy. “If I could answer you, I would,” he said. “But I can’t.”
Since Thailand’s absolute monarchy was abolished in 1932, immediate members of the royal family have not run for high office. The country’s political system has for decades involved a cut and thrust between powerful political forces committed to elections and a military that has at times deemed the ballot box harmful to the country. The military has staged a dozen successful coups.
Rumors about Ms. Ubolratana’s close ties with the Shinawatra family intensified last year when she was pictured with Mr. Thaksin, a former prime minister, and Yingluck Shinawatra, his sister and another former prime minister.
Both brother and sister have been convicted of corruption-linked crimes in absentia and are living in exile. A 2006 military putsch ended the tenure of Mr. Thaksin, whose political base came from Thailand’s rural poor. Every election this century has been won by forces loyal to Mr. Thaksin.
Late last month, Ms. Ubolratana, who still sometimes referred to as a princess despite her marriage and divorce to a foreigner, made a high-profile pilgrimage to nine Buddhist temples, something that politicians often do to pray for good fortune in electoral contests.
She is expected to regain her official royal titles when her brother is formally crowned in May.
Their father, King Bhumibol Adulyadej, was the world’s longest-reigning monarch until his death in 2016. Although he had no formal political role, during his seven decades on the throne, King Bhumibol was seen as a unifying force for a nation frequently troubled by coups and deadly political violence.
