The princess - the daughter of Crown Prince Maha Vajiralongkorn and Princess Soamsavali - joined the drive at a ceremony which marked her position as a Goodwill Ambassador for the United Nations Development Fund for Women (UNIFEM).
She said: "I am confident that, with our concerted efforts, the UNIFEM campaign will certainly draw a huge number of signatures from the public showing the strength of Thailand's one clear voice towards ending the violence against women."
The royal gave out cards bearing the words "Say NO" to those who attended the event in Bangkok, which included ministers, senior Government officials and dignitaries, and asked them to back the campaign and encourage their peers to get involved too.
Princess Bajrakitiyabha was asked to be a Goodwill Ambassador following her work promoting women's rights in Thailand.
UNIFEM Executive Director Ines Alberdi, via a video message from New York, said: "I am honored that Your Royal Highness has agreed to become UNIFEM's Goodwill Ambassador in Thailand and to support our efforts to advance women's empowerment."
"In particular, I would like to thank you for your willingness to add your name to UNIFEM's Say NO to Violence against Women campaign today and to make ending violence against women a focus of your work with us."
