He was born as Decimus Junius Brutus, gaining the Albinus when he was adopted by A. Postumius Albinus, the consul for 99 BC, but is now generally known as Decimus Brutus, to separate him from the more famous Brutus, M. Junius Brutus.
In 56 BC the young Decimus Brutus was given command of a fleet that Caesar had created to deal with the Veneti, a Gallic tribe that lived on the coast of Brittany, and relied on their fleets for safety. Brutus won a naval battle against the Veneti, perhaps the first known in the Atlantic. We next read of Brutus during the fight against Vercingetorix, where he was involved in the siege of Alesia.
By 50 BC Brutus was back in Rome, where he was married. At the start of the Civil War in 49 BC he sided with Caesar, and was appointed to command a fleet that Caesar had built to take part in the siege of Massilia (Marseille). D. Brutus won two naval battles off Massilia during the siege, playing a major part in its successful conclusion. He was then given command of Further Gaul (the area conquered by Caesar), where he won a victory over the Bellovaci.
In 45 BC Decimus Brutus returned to Rome with Caesar. He was promised the governorship of Cisalpine Gaul, the praetorship for 44 BC and the consulship for 44 BC. Despite all of these marks of favour he decided to join the conspiracy against Caesar, and on the Ides of March was chosen to lead Caesar to the Senate house.
Decimus Brutus was the probable target of Caesar's famous last words, 'et tu, Brute?', or 'and thou, Brutus'. This phrase, probably spoken in Greek, is mentioned by Cassius Dio and Suetonius, but in both cases only to deny that the words were said!
In the aftermath of Caesar's murder D. Brutus moved to his province. Power in Rome soon slipped out of the hands of the assassins. In 44 BC Mark Antony was granted Cisalpine Gaul by the Roman people, but when he attempted to take command of his new province D. Brutus refused to hand it over. Antony led an army across the Rubicon, catching Brutus by surprise. He retreated into Mutina, where he was besieged until April 43 BC. In that month an army led by the new consuls for the year, and supported by the young Octavianus (the future Augustus), defeated Antony in battle outside Mutina. Both of the consuls were killed in the battle, leaving D. Brutus officially in charge. For a short period D. Brutus represented the best chance for the restoration of the Roman Republic.
This didn't last for long. Antony escaped from the battlefield and managed to gain control of Marcus Lepidus's army in Gaul. D. Brutus found himself trapped between Antony and Octavianus. Three of his legions deserted him and joined Antony. At this point D. Brutus decided to march around the coast to join M. Brutus in Macedonia, but his remaining troops began to desert him. D. Brutus was betrayed to Antony by Camillus, a Gallic chief, and murdered on Antony's orders.