Magni was the eldest of the Bronzebeard brothers which makes him the heir to the throne. The dwarves were known to mine the treasure beneath the ground. It was Magni who suggested to the Dwarves that they use archaelogy too. Under his leadership, the dwarves of Ironforge joined the Alliance of Lordaeron. King Magni was saddened by his younger brother Muradin's supposed death at Arthas' hands but still continued to lead his people. Magni agreed to forge the Ashbringer for Alexandros Mograine to avenge his brother.
After the Third War, Magni Bronzebeard learned that his daughter was captured by Dagran Thaurissan. Believing his daughter Moira was under a spell, King Bronzebeard sent a task force of adventurers to Blackrock Depths to save her and kill Dagran Thaurissan. After Thaurissan was assassinated, the task force reported to Magni Bronzebeard that Moira was actually in love with Dagran and refuses to come back home. He was shocked to learn that Moira had a child with Thaurissan who later be Magni's heir and the leader of the Dark Iron Dwarves. Bronzebeard later learned that Muradin was still alive and reunited with him and his other younger brother Brann.
When the Cataclysm arrived in Azeroth, Magni sacrificed himself to save Ironforge from the earthquakes by activating stone tablets, He was later turned into a diamond stone statue and a funeral was held for him that was even attended by a few members of the Horde.