Ibn Abbas was a boy when the Prophet died, which means his whole adult life falls inside the conflicts that followed. He held Basra as governor for his cousin Ali, and the sources also carry a dispute about the treasury there and about his leaving the post, told in ways that clearly reflect later partisanship.
The episode most often credited to him is the negotiation at Harura. When a body of Ali's army broke away over the decision to accept arbitration, becoming the first Kharijites, Ibn Abbas was sent to argue with them. The reports have him address their three specific objections point by point rather than denouncing them, and return with a large number persuaded. Whether the numbers are reliable or not, the episode is remembered as an argument won by engaging with the case rather than by force, which is rare in that decade.
Later he declined to give allegiance to Ibn al-Zubayr during the second civil war and was expelled from Mecca to Ta'if, where he died around 687. He was blind in his last years.
One further fact shapes everything written about him. The Abbasid caliphate, which held power from 750, took its name and its legitimacy from descent through him. A dynasty with an interest in the standing of its ancestor patronised scholarship for five centuries, and the effect on the volume of material transmitted in his name is impossible to separate out. The honorific titles, the interpreter of the Quran and the rabbi of this community, are genuine early usage, and they were also extremely convenient.