Born in Korea, Julia Ota was brought to Japan during the Japanese invasions of Korea (1592–98) by the leading Japanese general Konishi Yukinaga. Yukinaga was a devout Christian, and he raised her as his own in his Christian household where she lived with Yukinaga's wife. She was baptised by the Jesuit father Pedro Morejon in 1596 in Uto. Thus "Julia" was her baptismal name while "Ota" was the Japanese name given to her as found in Jesuit records—her original Korean name was not recorded.
After the downfall of Konishi Yukinaga at the Battle of Sekigahara in 1600, Julia Ota was made to serve Yukinaga's vanquisher Tokugawa Ieyasu as a lady-in-waiting in his household (奥方ノ御物仕). In this role she kept in contact with the missionaries of Fushimi Castle and Sunpu Castle and continued practicing her faith, while also influencing other servants of Ieyasu's household to convert to Christianity. However, she grew restless as rumours of religious persecution in Edo reached her ears, and she made arrangements to distribute her money and belongings to the poverty-stricken Christians.
The Okamoto Daihachi incident came to light in 1612, which made Ieyasu suspicious of Christianity's influence on his subjects. He was thus quite alarmed to find many of his own servants were Christians, chief among them Julia Ota. She refused to recant her faith when presented with an ultimatum and would rather shave her head to renounce her attachments to the world. So Ieyasu banished her and other like-minded servants from his household and exiled her to the Izu Islands. Julia Ota was first sent to Izu Ōshima, then Nii-jima, and finally Kōzu-shima. Wherever she went, she became admired for her charity and evangelism, and she was revered as divinity on the islands up after her death up to the 20th century.
In 1619, she left Kōzu-shima and took refuge in Nagasaki, apparently having received a pardon around the time Ieyasu died. There, despite orders from the Nagasaki bugyō, she did not cease her evangelical activities and was driven out of her home multiple times. According to a letter by the Jesuit priest Francisco Pacheco dated February 15, 1622, Julia Ota was receiving financial support from Pacheco in Osaka. This was the last known record of Ota.
Despite evidence to the contrary, there remains a number of gravesites on the Izu Islands purporting to be that of Julia Ota. On Izu Ōshima, a shrine was raised upon her alleged grave, making it a rare case of a Shinto shrine being raised over a Christian grave, and where a Christian soul was revered as a kami. Another purported grave site on Kōzu-shima was commemorated by a large crucifix erected on the island in 1958 by Japanese and Korean Christians, and a festival is held in her honour in May each year on the island. In 1972, earth from her alleged grave on Kōzu-shima was brought to Seoul's Jeoldu-san, a memorial shrine for Korean Christians, as a symbolic homecoming.
- Ruiz de Medina 1988, p. 60.
- Ruiz de Medina 1988, p. 58 note 14.
- Gonoi, Takashi. "ジュリアおたあ (Julia Ota)". Asahi Nihon Rekishi Jinbutsu Jiten (in Japanese). Asahi Shimbun Publications. Retrieved 29 October 2017.
- Boxer 1951, p. 315.
- "Pilgrims revere Korean-born woman expelled from Tokyo for her faith". ucanews.com. Italy. 5 June 1985. Retrieved 30 October 2017.
- Boxer 1951, p. 492.
- Ruiz de Medina 1988, p. 61.
- Turnbull 2013, p. 113.
- Roney, Stephen K. (19 January 2001). "Seoul shrine honors Korea's 'Helen'". Korea Herald. Archived from the original on 24 February 2001. Retrieved 29 October 2017.
- Boxer, C. R. (1951). The Christian Century in Japan: 1549–1650. University of California Press. GGKEY:BPN6N93KBJ7.
- Turnbull, Stephen (2013) [First published 1998]. The Kakure Kirishitan of Japan: A Study of Their Development, Beliefs and Rituals to the Present Day. Routledge. ISBN 9781136751592.
- Ruiz de Medina, Juan G. (1988). "History and Fiction of Ota Julia" 韓国人キリシタン大田ジュリアをめぐって. Kirisutokyo-shigaku (in Japanese). 42. ISSN 0453-9389.