King Usermaatre Setepenre or Usimare Setepenamun Shoshenq III rules Egypt's 22nd Dynasty for 39 years according to contemporary historical records.

Two Apis Bulls were buried in the fourth and 28th years of his reign and he celebrated his Heb Sed Jubilee in his regnal year 30.

Little is known of the precise basis for his successful claim to the throne since he was not a son of Osorkon II and Shoshenq's parentage and family ties are unknown.

From Shoshenq III's eighth regnal year, his reign was marked by the loss of Egypt's political unity, with the appearance of Pedubast I at Thebes.

Henceforth, the kings of the 22nd Dynasty only controlled Lower Egypt.

The Theban High Priest Osorkon B (the future Osorkon III) did date his activities at Thebes and (Upper Egypt) to Shoshenq III's reign but this was solely for administrative reasons since Osorkon did not declare himself king after the death of his father, Takelot II.

On the basis of Osorkon B's well known Chronicle, most Egyptologists today accept that Takelot II's 25th regnal year is equivalent to Shoshenq III's 22nd year.