Decimus Brutus was a distant cousin of Julius Caesar, and on several occasions Caesar expressed how he loved Brutus like a son. Ronald Syme argued that if a Brutus was the natural son of Caesar, Decimus was more likely than Marcus (another distant cousin). Decimus was named an heir in the second degree in Caesar's will.
Decimus Brutus spent his youth mainly in the company of Publius Clodius, Gaius Curio and Mark Antony. His mother was Sempronia Tuditani, wife of Decimus Junius Brutus who was consul in 77 BC. He was adopted by Aulus Postumius Albinus, but kept his own family name, only adding his adoptive father's cognomen Albinus.
He served in Caesar's army during the Gallic wars and was given the command of the fleet in the war against the Veneti in 56 BC. In a decisive sea battle, Decimus Brutus succeeded in destroying the Veneti's fleet. Using sickle-like hooks fitted on long poles, Decimus Brutus attacked the enemy's sails, leaving them immobilized and easy prey to Roman boarding parties. He also served against Vercingetorix in 52 BC.
When the Republican Civil War broke out, Decimus Brutus sided with his commander, Caesar, and was entrusted once again with fleet operations. Richard Billows argued that Caesar loved Decimus Brutus almost as a son.
The Greek city of Massilia (present-day Marseille) sided with Pompey the Great, and Caesar, hastening to reach Hispania and cut Pompey off from his legions, left Decimus Brutus in charge of the naval blockade of Massilia. Within thirty days, Decimus Brutus built a fleet from scratch and secured the capitulation of Massilia.
When Caesar returned to Rome as dictator after the final defeat of the Republican faction in the Battle of Munda (45 BC), Marcus Brutus joined the conspiracy against Caesar, after being convinced by Cassius and Decimus. In 44 BC, Decimus was made Praetor Peregrinus by personal appointment of Caesar and was designated to be the governor of Cisalpine Gaul in the following year.
On the Ides of March (March 15), when Caesar decided not to attend the Senate meeting due to the concerns of his wife, he was persuaded to attend by Decimus Brutus, who escorted him to the senate house, and neatly evaded Mark Antony, who wished to tell Caesar of the assassination plot. After Caesar was attacked by the first assassin, Servilius Casca, Decimus and the rest of the conspirators attacked and killed him. In all, Caesar suffered approximately 23 stab wounds. According to Nicolaus of Damascus, Decimus Brutus was the last to strike Caesar, stabbing him in the side.
The assassins received an amnesty the next day, issued by the senate at the instigation of Mark Antony, Caesar's fellow consul. But the situation was not peaceful, Rome's population and Caesar's legionaries wanted to see the conspirators punished. The group decided to lie low, and Decimus used his office of Praetor Peregrinus to stay away from Rome.
The climate of reconciliation soon passed and slowly the conspirators were starting to feel the strain of the assassination. Thus, at the beginning of 43 BC, Decimus Brutus hurried to Gallia Cisalpina, the province assigned to him as pro-praetor, and started to levy his own troops. He was ordered by the Senate to surrender his province to Antony but refused. This was the act of provocation to which Antony was only too happy to respond. With his own political situation on the verge of disaster and himself declared public enemy, defeating Decimus Brutus was a way for Antony to regain his ascendancy and get control of the strategically important Italian Gaul.
In 43 BC Decimus Brutus occupied Mutina, laying in provisions for a protracted siege. Antony obliged him, and blockaded Decimus Brutus' forces, intent on starving them out.
Nevertheless, the consuls of the year, Aulus Hirtius and Gaius Pansa, marched northward to raise the siege. Guided by Cicero (whose Philippics date from this time), the Senate was inclined to view Mark Antony as an enemy. Caesar Octavian, the nineteen-year-old heir of Caesar, and already raised to the rank of propraetor, accompanied Gaius Pansa north. The first confrontation occurred on April 14 at the battle of Forum Gallorum, where Antony hoped to deal with his opponents piecemeal. Antony defeated the forces of Gaius Pansa and Octavian, which resulted in Pansa suffering mortal wounds; however, Antony was then defeated by a surprise attack from Hirtius. A second battle on 21 April at Mutina resulted in a further defeat for Antony and Hirtius' death. Antony withdrew, unwilling to become the subject of a double circumvallation as Caesar had done to Vercingetorix at Alesia.
With the siege raised, Decimus Brutus cautiously thanked Octavian, now commander of the legions that had rescued him, from the other side of the river. Octavian coldly indicated he had come to oppose Antony, not aid Caesar's murderers. Decimus Brutus was given the command to wage war against Antony, but many of his soldiers deserted to Octavian.
His position deteriorating by the day, Decimus Brutus fled Italy, abandoning his legions. He attempted to reach Macedonia, where Marcus Junius Brutus and Gaius Cassius Longinus had stationed themselves but was executed en route by a Gallic chief loyal to Mark Antony.
Several letters written by Decimus Brutus during the last two years of his life are preserved among Cicero's collected correspondence.
In Shakespeare's Julius Caesar, Decimus Brutus is mistakenly called "Decius".
In Allan Massie's 1993 book entitled Caesar, Decimus Junius Brutus Albinus narrates his story and reason for joining in Caesar's assassination while being held captive by the Gallic chief.
Decimus Brutus is an important character in Caesar and The October Horse by Colleen McCullough. In these novels, he and Gaius Trebonius are portrayed as the real leaders of the assassination conspiracy.
In Conn Iggulden's Emperor Series the historical figures of Decimus Brutus and Marcus Brutus are blended together into the one character named Marcus Brutus.
In Ben Kane's books The Forgotten Legion, The Silver Eagle, and Road To Rome, Decimus Brutus is shown as a fairly major character to the plot and the rest of the book as Fabiola's lover.
In Robert Harris' novel, Dictator, it is Decimus, not Marcus Junius, who is the Brutus targeted during Caesar's assassination by Caesar's alleged accusatory words, "Even you?" The phrase, more often rendered as "Et tu," is immortalized in Shakespeare's Julius Caesar.