He succeeded to the throne at age six, after the death of Nemtyemsaf I. Pepi II's reign marked a sharp decline of the Old Kingdom.

He was traditionally thought to be the son of Pepi I and Queen Ankhesenpepi II, but the South Saqqara Stone annals record that Merenre had a minimum reign of 11 years.

Several 6th Dynasty royal seals and stone blocks – the latter of which were found within the funerary temple of Queen Ankhesenpepi II, the known mother of Pepi II – were discovered in the 1999–2000 excavation season at Saqqara, which demonstrate that she also married Merenre after Pepi I's death and became this king's chief wife.

An alabaster statuette in the Brooklyn Museum depicts a young Pepi II, in full kingly regalia, sitting on the lap of his mother.

A glimpse of the personality of the pharaoh while he was still a child can be found in a letter he wrote to Harkhuf, a governor of Aswan and the head of one of the expeditions he sent into Nubia.

[17] Some, like R. S. Bianchi, think that it is a work of archaizing literature and dates to the 25th Dynasty referring to Shabaka Neferkare, a Kushite pharaoh.

[18] The decline of the Old Kingdom arguably began before the time of Pepi II, with nomarchs (regional representatives of the king) becoming more and more powerful and exerting greater influence.

Their influence was extensive, both sisters bearing sons who were chosen as part of the royal succession: Merenre Nemtyemsaf I and Pepi II himself.

Large and expensive tombs appear at many of the major nomes of Egypt, built for the reigning nomarchs, the priestly class and other administrators.

Their increasing wealth and independence led to a corresponding shift in power away from the central royal court to the regional nomarchs.

Pepi II is often mentioned as the longest reigning monarch in history, due to a 3rd-century BC account of Ancient Egypt by Manetho, which accords the king a reign of 94 years; this has, however, been disputed by some Egyptologists such as Hans Goedicke and Michel Baud due to the absence of attested dates known for Pepi II after his 31st count (Year 62 if biennial).

At the present time, the latest written source contemporary with Pepi II dates from the "Year after the 31st Count, 1st Month of Shemu, day 20" from Hatnub graffito No.7 (Spalinger, 1994),[20] which implies, assuming a biennial cattle count system, that this king had a reign of at least 62 complete or partial years.

For Mesopotamia from at least this early until virtually the Persian conquest, numerous localized synchronisms play vital roles in absolute dating, but seldom affect the duration of individual dynasties.

[26] This situation could have produced a succession crisis and led to a stagnation of the administration, centered on an absolute yet aging ruler who was not replaced because of his perceived divine status.

A later, yet better documented, example of this type of problem is the case of the long reigning Nineteenth Dynasty pharaoh Ramesses II and his successors.

[citation needed] It has been proposed that the 4.2 kiloyear event be linked to the collapse of the Old Kingdom in Egypt, though current resolution of evidence is not sufficient to make an assertion.

[27][28] In the past it had been suggested that Ipuwer the sage served as a treasury official during the last years of Pepi II Neferkare's reign.

[29][30] The Ipuwer Papyrus was thought by some to describe the collapse of the Old Kingdom and the beginning of the Dark Age, known to historians as the First Intermediate Period.

Gerhard Fecht [de] showed through philological interpretation and revision of the relevant passages that this is indeed a discussion with a deity.

[30] The admonitions are thought to harken back to the First Intermediate Period and record a decline in international relations and a general impoverishment in Egypt.

An interesting feature is that after the north chapel and the wall was completed, the builders tore down these structures and enlarged the base of the pyramid.

[35][36] The mortuary temple adjacent to the pyramid was decorated with scenes showing the king spearing a hippopotamus and thus triumphing over chaos.

According to Manetho and the Turin King List, he was succeeded by his son Merenre Nemtyemsaf II, who reigned for just over a year.