Brutus lost at Philippi on October 23, 42 BC. He was the last of Caesar's assassins still in the field, and Mark Antony and Octavian broke his army and forced him to take his own life. The Roman Republic died with him.
The two sides had fought once already. The first battle, three weeks before, had gone against Cassius, Brutus's partner, and he had killed himself in despair. The second battle came when Brutus, short of supplies and urged on by his own men, offered fight again. He lost again.
The defeat was total. Brutus fled the field with a few followers and fell on his sword before dawn, and the army that had fought to keep the Senate sovereign scattered. The cause was dead, and no one came to take it up.
The victory went to Antony and Octavian. They shared the spoils. They divided the Roman world between them, and then they fought each other, and Octavian won and became Augustus, the first emperor. The republic that Brutus died to save was never restored.
The battle fixed the shape of Rome. A city that had been governed by elected magistrates and a Senate became the property of one family, and the empire that followed lasted five centuries. Brutus chose death over submission, and the choice settled nothing.