Onesimus, bishop of Byzantium (a runaway slave and early Christian convert mentioned in the New Testament of the Christian Bible).
Onesimus may also refer to:
- Onesimus, the Sudanese slave of Boston Puritan Cotton Mather
- Onesimos Nesib (ca 1856-1931), translated the Bible into the Ethiopian Oromo language
- Onesimus of Kiev - a monk and saint - see Abraham and Onesimus of Kiev
- Onesimos (vase painter) (fl ca. 505 – ca. 480 BCE)
- Onesimus (book) (1882), a book by Edwin Abbott Abbott
- Onesimus; A Quest For Freedom, (1992) a Christian video game.