The first battle in which he could take part was the Battle of Khandaq, while he was just 15. Although he is reported to have been taking part in almost 14 to 18 battles, he seems not be have played any specific roles.

According to a narration by al-Bara' himself, when the Prophet (s) has sent Khalid b. Walid to Yemen in order to spread the message of Islam, al-Bara' was accompanying his group, and as this mission was given over to Imam Ali (a), al-Bara' joined him.

Taking Part in Conquests

According to some narrations, during the last part of 'Umar's caliphate or the first part of Uthman's caliphate, al-Bara' b. 'Azib has taken part in or led some battles, conquering some parts of Iran, like: Rey, Qumis, Zanjan, Abhar and Qazvin. One of the conquests of Rey was also under his commander-ship. He managed to agree on peace with the people of Abhar and could make peace with the people of Qazvin with difficulty. He had to, however, conquer Zanjan through battle. All this said, it must be mentioned that at least in one narration of the "conquest narrations", he has been mistaken for Bara' b. Malik.

Giving Allegiance to Imam Ali (a)

It is said that al-Bara' b. 'Azib was among those who pledged allegiance to Imam Ali (a). Although there is no narration indicating his participation in the battles during Imam Ali's caliphate, but based on one narration, beside taking part in the Battles of Jamal, Siffin and Nahrawan, he was also appointed by Imam Ali (a) in the Battle of Nahrawan to take over the mission of turning the Kawarij to Imam Ali's camp.

Narrations

Al-Bara' narrated some hadiths from the Prophet (s). Some of these narrations show how interested he was in the prophetic accounts, hadiths and life.

Imam al-Husayn's Martyrdom

In his book al-Irshad, al-Shaykh al-Mufid narrates from Isma'il b. Ziyad, "One day Imam Ali (a) told al-Bara' b. 'Azib: 'O al-Bara'! my son will be martyred and you won't help him, although you'll be alive on that day'". After the Battle of Karbala, al-Bara' said: "What Ali (a) had said was realized, because his son was martyred and I didn't help him". Then he regretted deeply for that.

References

The material for this article is mainly taken from براء بن عازب in Farsi Wikishia.