Hattusili belonged to the royal family of Hatti. His father was Mursili II, and his elder brother Muwatalli II became Great King before him. The younger prince rose through military and administrative responsibilities in the northern territories, where Hakpis became an important centre of his authority. These appointments belonged to his brother's reign, not to an uncomplicated inheritance of the northern kingdom from his father. His career placed him close to power without initially making him its supreme holder. When Muwatalli fought Ramesses II at Kadesh in 1274 BCE, Hattusili served on the Hittite side. He was not yet the Great King who would later negotiate with the pharaoh.

After Muwatalli's death, his son Urhi-Teshub took the throne as Mursili III. Hattusili initially supported his nephew, but their relationship deteriorated as the new king reduced his uncle's authority. The dispute ended in Hattusili's victory and the deposition of Mursili III. The capital had already been returned from Tarhuntassa to Hattusa during the nephew's reign, before Hattusili became Great King. What followed was a problem of legitimacy. Winning a struggle within the royal family did not automatically persuade every subject or foreign court that the victor was the rightful king.

The Apology gives that problem a religious answer. It recounts Hattusili's life under the protection of the goddess identified in the text as Ishtar, associated with the Hurrian Shaushga. Illness, service, conflict and eventual kingship become stages in a career directed by divine favour. The narrative is valuable evidence for the way the ruler presented himself, but it is not an impartial judgement on his nephew. Dreams and divine promises belong to the king's account of his own legitimacy. Calling the work an apology does not mean he was expressing modern remorse. It is a defence of conduct, designed to make a controversial change of ruler appear just.

Peace with Egypt became one of the achievements of his reign. The agreement with Ramesses II is conventionally dated to 1259 BCE, well after the battle of Kadesh. It pledged peaceful relations, support against enemies and the return of certain fugitives. Oaths invoked the gods of both sides. The treaty was recorded on silver tablets, but those originals have not survived: the finds from Hattusa are clay copies, while Egyptian monumental versions were carved in hieroglyphs. Its importance lies in the unusually rich survival of evidence from both kingdoms, not in a secure claim that humanity had never made a peace agreement before. The treaty joined ideals of lasting brotherhood to the practical security of two royal houses.

Puduhepa was central to the world in which that diplomacy operated. Hattusili's own narrative places their marriage at Lawazantiya and presents it as favoured by the goddess. It does not require the romantic claim that he first met his future wife in a dream. As queen, Puduhepa exchanged letters with Ramesses II and with his queen Nefertari. Royal kinship language made distant courts sound like one family, even when each was pursuing its own interests. A daughter of Hattusili and Puduhepa later married Ramesses and took the Egyptian name Maathorneferure. That marriage, in the mid-1240s BCE, strengthened a relationship already established through negotiation.

The deposed Mursili III remained a difficulty. A rival claimant could seek support outside Hatti, and his movements became part of the tense correspondence between royal courts. Such tensions show why an alliance needed more than a grand declaration. It depended on messengers, letters, gifts and continuing decisions by people who did not always trust one another. Hattusili was succeeded by his son Tudhaliya IV. The tablets recovered from Hattusa preserve documents from a wider royal and religious archive, not merely one king's private library. Among them, the Apology and diplomatic correspondence allow the later reader to compare public justification with the business of maintaining a kingdom.