Umar was born in Mecca to the Banu Adi clan, which was responsible for arbitration among the tribes. His father was Khattab ibn Nufayl and his mother was Hantama bint Hisham, from the tribe of Banu Makhzum. In his youth he used to tend to his father's camels in the plains near Mecca. His merchant father was famed for his intelligence among his tribe. Umar himself said: "My father, Al-Khattab was a ruthless man. He used to make me work hard; if I didn't work he used to beat me and he used to work me to exhaustion."

Despite literacy being uncommon in pre-Islamic Arabia, Umar learned to read and write in his youth. Though not a poet himself, he developed a love for poetry and literature. According to the tradition of Quraish, while still in his teenage years, Umar learned martial arts, horse riding and wrestling. He was tall, physically powerful and a renowned wrestler. He was also a gifted orator who succeeded his father as an arbitrator among the tribes.

Umar became a merchant and made several journeys to Rome and Persia, where he is said to have met various scholars and analyzed Roman and Persian societies. As a merchant he was unsuccessful. Like others around him, Umar was fond of drinking in his pre-Islamic days.

Initial hostility to Islam

In 610 Muhammad started preaching the message of Islam. Like many others in Mecca, Umar opposed Islam and he even threatened to kill Muhammad. He resolved to defend the traditional polytheistic religion of Arabia. He was adamant and cruel in opposing Muhammad and very prominent in persecuting Muslims. He recommended Muhammad's death. He firmly believed in the unity of the Quraish and saw the new faith of Islam as a cause of division and discord.

Due to persecution, Muhammad ordered some of his followers to migrate to Abyssinia. When a small group of Muslims migrated Umar became worried about the future unity of the Quraish and decided to have Muhammad assassinated.

Conversion to Islam

Umar converted to Islam in 616, one year after the Migration to Abyssinia. The story was recounted in Ibn Ishaq's S?rah. On his way to murder Muhammad, Umar met his best friend Nua'im bin Abdullah who had secretly converted to Islam but had not told Umar. When Umar informed him that he had set out to kill Muhammad, Nua'im said, “By God, you have deceived yourself, O Umar! Do you think that Banu Abd Manaf would let you run around alive once you had killed their son Muhammad? Why don't you return to your own house and at least set it straight?"

Nuaimal Hakim told him to inquire about his own house where his sister and her husband had converted to Islam. Upon arriving at her house, Umar found his sister and brother-in-law Saeed bin Zaid (Umar's cousin) reciting the verses of the Quran from sura Ta-Ha. He started quarreling with his brother-in-law. When his sister came to rescue her husband, he also started quarreling with her. Yet still they kept on saying "you may kill us but we will not give up Islam". Upon hearing these words, Umar slapped his sister so hard that she fell to the ground bleeding from her mouth. When he saw what he did to his sister, he calmed down out of guilt and asked his sister to give him what she was reciting. His sister replied in the negative and said "You are unclean, and no unclean person can touch the Scripture." He insisted, but his sister was not prepared to allow him to touch the pages unless he washed his body. Umar at last gave in. He washed his body and then began to read the verses that were: Verily, I am Allah: there is no God but Me; so serve Me (only), and establish regular prayer for My remembrance (Quran 20:14). He wept and declared, "Surely this is the word of Allah. I bear witness that Muhammad is the Messenger of Allah." On hearing this, Hadhrat Khabbab came out from inside and said: "O, Umar! Glad tidings for you. Yesterday Muhammad prayed to Allah, 'O, Allah! Strengthen Islam with either Umar or Abu Jahl, whomsoever Thou likest.' It seems that his prayer has been answered in your favour."

Umar then went to Muhammad with the same sword he intended to kill him with and accepted Islam in front of him and his companions. Umar was 39 years old when he accepted Islam.

Following his conversion, Umar went to inform the chief of Quraish, Amr ibn Hish?m, about his acceptance of Islam. According to one account, Umar thereafter openly prayed at the Kaaba as the Quraish chiefs, Amr ibn Hish?m and Abu Sufyan ibn Harb, reportedly watched in anger. This further helped the Muslims to gain confidence in practicing Islam openly. At this stage Umar even challenged anyone who dared to stop the Muslims from praying, although no one dared to interfere with Umar when he was openly praying.

Umar's conversion to Islam granted power to the Muslims and to the Islamic faith in Mecca. It was after this event that Muslims offered prayers openly in Masjid al-Haram for the first time. Abdullah bin Masoud said,

Umar's embracing Islam was our victory, his migration to Medina was our success, and his reign a blessing from Allah. We didn't offer prayers in Al-Haram Mosque until Umar had accepted Islam. When he accepted Islam, the Quraysh were compelled to let us pray in the Mosque.

Migration to Medina

In 622 CE, due to the safety offered by Yathrib (later renamed Med?nat an-Nab?, or simply Medina), Muhammad ordered his followers to migrate to Medina. Most Muslims migrated at night fearing resistance from Quraish at their migration, but Umar is reported to have left openly during the day saying: "Any one who wants to make his wife a widow and his children orphans should come and meet me there behind that cliff." Umar migrated to Medina accompanied by his cousin and brother-in-law Saeed ibn Zaid.

Life in Medina

When Muhammad arrived in Medina, he paired each immigrant (Muhajir) with one of the residents of the city (Ansari), joining Muhammad ibn Maslamah with Umar, making them brothers in faith. Later in Umar's reign as caliph, Muhammad ibn Muslamah would be assigned the office of Chief Inspector of Accountability. Muslims remained in peace in Medina for approximately a year before the Quraish raised an army to attack them.

Early battles after the migration

In 624 Umar participated in the first battle between Muslims and Quraish of Mecca i.e., the Battle of Badr. In 625 he took part in the Battle of Uhud. In the second phase of the battle, when Khalid ibn Walid's cavalry attacked Muslims at the rear changing the victory of Muslims to defeat, rumours of Muhammad's death were spread and many Muslim warriors were routed from the battlefield, Umar too was initially routed but hearing that Muhammad was still alive he went to Muhammad at the mountain of Uhud and prepared for the defences of the hill to keep the army of Quraish from approaching the hilltop. Later in the year Umar was a part of a