Japan's Imperial Household Agency will announce plans for the engagement of Princess Ayako.
The princess is the third daughter of the late Prince Takamado, Emperor Akihito's cousin. She is 27.
Her prospective fiance, Kei Moriya who is 32, works at a major shipping company in Tokyo.
He and his parents are said to have been invited to a party at the princess's residence in April.
Sources say the princess's mother has given her blessing to the couple, and that the Emperor and Empress have also been informed of their wish to get engaged.
Agency officials say a wedding ceremony will be held at Tokyo's Meiji Jingu shrine on October 29th.
Marriage of male members of the Imperial family requires approval by the Imperial House Council, headed by the Prime Minister.
But the step is not necessary for female members. Their engagement becomes official after a betrothal ceremony, called the Nosai-no-Gi.
Princess Ayako wrote on her 20th birthday in 2010 that she loves children, and hopes to marry one day. She said she wants to nurture a warm family filled with laughter, with a person she can respect.
Princesses must leave the Imperial household upon marriage but a serious decline of members could trigger fresh debate over the system.
Princess Ayako's elder sister, Noriko, left the family when she married a Shinto priest in 2014.
Announcements were made last year for the planned engagement of Princess Mako, the eldest daughter of Prince Akishino, to a friend from college.