Augustus, the first Roman emperor, was born in Rome on 23 September 63 BC as Gaius Octavius. In his early childhood he was raised by his parents, Gaius Octavius and Atia, but after the elder Octavius's death he was raised in part by his stepfather Lucius Marcius Philippus and his grandmother Julia. In his youth he was provided an education in Greek and Latin rhetoric, mathematics, and philosophy.

Dictator Julius Caesar, Octavius's great-uncle, helped foster his early career after Octavius donned the toga virilis at age 15 to mark his coming of age as an adult citizen. Caesar had Octavius elected to the College of Pontiffs, ride in his chariot during a triumph, and accompany him on a military campaign in Hispania. Caesar named Octavius as his primary heir in his will, but was assassinated on the Ides of March in 44 BC while Octavius was studying and undergoing military training at Apollonia in Illyria. Afterwards, Octavius sailed back to Italy to claim his inheritance as the rightful heir to Caesar, and is labeled by historians at this stage with the name Octavian. Ultimately victorious after a series of civil wars, he would eventually be named Augustus by the Roman Senate in 27 BC, an event that traditionally marks the end of the Roman Republic and beginning of the Roman Empire.

Augustus was born Gaius Octavius in Rome on 23 September 63 BC. Historians Anne-Marie Lewis and Karl Galinsky explain how there is scholarly debate surrounding Octavius's precise date of birth. Evidence that it had occurred on 22 September is based on statements by historians such as Suetonius and Velleius Paterculus, though Cassius Dio affirms it occurred on 23 September, and confusion also stems from the transition of using the early Republican Roman calendar to using the Julian Calendar during Octavius's lifetime. Most Roman histories gloss over the childhood of Octavius. Some details about his upbringing from his now-lost autobiography were preserved by Suetonius. However, the majority of information is preserved in a biography composed by Nicolaus of Damascus around 20 BC. This biography has only partially survived in 10th-century Byzantine excerpts, namely the Excerpta Constantiniana. Appian and Cassius Dio provide information about the rise of Augustus as a triumvir, while Cassius Dio and Tacitus focus on Augustus's role as princeps and reign as the first Roman emperor.

Octavius was a member of the respectable, but undistinguished, equestrian Octavii family through his father, also named Gaius Octavius. The younger Octavius was also the great-nephew of Julius Caesar through his mother Atia. Octavius had two older siblings: a half sister, Octavia Major, from his father's first marriage, and a full sister, Octavia Minor. His paternal family was from the Volscian town of Velitrae (modern Velletri), approximately 40 kilometres (25 mi) south-east of the city. He was born at Ox Head, a small property on the Palatine Hill, very close to the Roman Forum. For at least a portion of his childhood he was raised in his family's hometown of Velitrae.

Octavius's paternal great-grandfather Octavius was a military tribune in Sicily during the Second Punic War. His grandfather was a banker. However, the family entered the senatorial ranks with Octavius's father, the elder Octavius, as its novus homo. The elder Octavius's entrance into the Senate came when he was appointed quaestor. He ascended the Cursus honorum as quaestor c. 73, aedile c. 64, and praetor in 61 BC, before being made proconsular governor of Macedonia, where he was proclaimed imperator for victories against the Thracian Bessi tribe on its frontiers.

In his childhood, Octavius may have received the cognomen "Thurinus" to commemorate his father's victory at Thurii over a rebellious band of slaves who were followers of Spartacus. Later, after he had taken the name of Caesar, his rival Mark Antony referred to him as Thurinus in order to belittle him. However, Antony did so by insinuating Octavius's great-grandfather was a mere plebeian rope-maker at Thurii, a dismissive insult based on social class.

The elder Octavius proved himself a capable administrator in Macedonia. Upon returning to Italy, before he could stand for consulship, he suddenly died in Nola in 59 BC, or in 58 BC, when Octavius was only four or five years old. In 58 BC Octavius's mother Atia married a former governor of Syria, Lucius Marcius Philippus. Philippus came from a leading family in Rome and was elected consul in 56 BC. According to Galinsky, as Octavius's stepfather, Philippus likely served as a role model in how to delicately navigate troubled political waters while preserving his personal wealth. It is also likely Octavius was partly raised by his grandmother Julia, the sister of Julius Caesar. When Julia died in 52 or 51 BC, Octavius delivered her funeral oration, his first major public appearance. Historian Patricia Southern adds that such a move carried political connotations for Octavius:

When his grandmother Julia died he delivered the funeral oration for her, probably aged about 11. It was his first public appearance. The content of the speech that Octavius made is unknown; it would not necessarily be absolutely accurate, since the main purpose was aggrandisement of the family. He would have known, or been told at this time, that Caesar had also made a similar funerary oration for his own aunt Julia, the wife of Gaius Marius, and he had done so at a time when connection with Marius was downright unhealthy, if not actually lethal. Funeral speeches were as much political gestures as they were acts of piety.