Ubaydah was the son of Al-Harith ibn Muttalib ibn Abdmanaf ibn Qusayy, hence a second cousin of Abd Allah ibn Abd al Muttalib and of Abu Talib ibn 'Abd al-Muttalib. His mother, Sukhayla bint Khuza'i, was from the Thaqif tribe. He had two full brothers, Al-Tufayl and Al-Husayn, who were more than twenty years younger than himself. Ubaydah's appearance is described as "medium, swarthy, with a handsome face."
In 622 Ubaydah and his brothers, together with their young cousin Mistah ibn Uthatha, joined the general emigration to Medina. They boarded with Abdullah ibn Salama in Quba until Muhammad allotted them some land in Medina. Muhammad gave Ubaydah two brothers in Islam: Abu Bakr's freedman Bilal ibn Rabah and an ansar named Umayr ibn Al-Humam.
Some say that Ubaydah was the first to whom Muhammad gave a banner on a military expedition; others say Hamza was the first. In April 623 Muhammad sent Ubaydah with a party of sixty armed Muhajirun to the valley of Rabigh. They expected to intercept a Quraysh caravan that was returning from Syria under the protection of Abu Sufyan ibn Harb and 200 armed riders. The Muslim party travelled as far as the wells at Thanyat al-Murra, where Sa`d ibn Abi Waqqas shot an arrow at the Quraysh. This is known as the first arrow of Islam. Despite this surprise attack, "they did not unsheathe a sword or approach one another," and the Muslims returned empty-handed.
You may cut off my leg, yet I am a Muslim.
I hope in exchange for a life near to Allah,
with Houris fashioned like the most beautiful statues,
with the highest heaven for those who mount there...
He was buried at Al-Safra.
He was the first Muslim to be killed in battle. Muslims regard him as a shahid, a word that cannot easily be translated into English but refers to a Muslim who dies in the course of his Islamic duties.
Following his death, his widow Zaynab became Muhammad's fifth wife.
He had a wife, Zaynab bint Khuzaimah. By her, he was the father of nine children: Muawiya, Awn, Munqidh, Al-Harith, Ibrahim, Rabta, Khadija, Suhaykhla, Amina and Safiya.