He took part in the Decepticon's first incursion on Earth because he liked the idea of destroying things. He went to the city that the final battle took place in with Barricade and the two Decepticons rampaged through the city, killed hundreds and nearly razing the place.
When Jazz, Ironhide and Ratchet arrived, Brawl considered retreating but instead decided to take them all on. After losing his missile launchers, his leg and his entire left arm, Brawl decided to fall back but came under attack by an enraged Bumblebee, who had lost his legs earlier on in the battle. Confused at being attacked by such a small foe, Brawl attempted to fight back but the slow and stupid clown of a Decepticon was soon brought down.
Thus ends the tragic tale of Brawl. His buddy Barricade saw Brawl die and fled the battle, and he would ironically suffer a similar fate during the Decepticon's third incursion.