Princess Bejaratana was born on 24 November 1925 in the Royal Grand Palace, Bangkok, the only child of King Vajiravudh (Rama VI) and Princess Suvadhana. Having seen his daughter only one time, the King died the following day. Her uncle, who became King Prajadhipok (Rama VII), performed the naming ceremony for the princess on 30 December.

Princess Bejaratana and her mother moved to Suan Hongsa Villa in Dusit Palace, where she received her education from a private tutor. They moved in with Queen Sri Savarindira (the Queen Dowager) during World War II, and the princess attended Rajani School until she was 12. She and her mother then moved to England, where she continued her education and took medication for her poor health. She first stayed at Fairhill Villa in Surrey, before settling in Brighton.