Amenmesse (also Amenmesses or Amenmeses) was the fifth pharaoh of the Nineteenth Dynasty in Ancient Egypt, possibly the son of Merneptah and Queen Takhat. Others consider him to be one of the innumerable sons of Ramesses II. Very little is known about this pharaoh, who ruled Egypt for only three to four years. Various Egyptologists date his reign between 1202 BC–1199 BC or 1203 BC–1200 BC with others giving an accession date of 1200 BC. Amenmesse means "born of or fashioned by Amun" in Egyptian. Additionally, his nomen can be found with the epithet Heqa-waset, which means "Ruler of Thebes". His royal name was Menmire Setepenre.

It is likely that he was not Merneptah's intended heir. Scholars Kenneth Kitchen and Jürgen von Beckerath have theorized that Amenmesse usurped the throne from Seti-Merneptah, who was Merneptah's son and crown prince and who should have been next in the line of royal succession. It is unclear how this would have happened. Kitchen has written that Amenmesse may have taken advantage of a momentary weakness of Seti-Merneptah or seized power while the crown prince was away in Asia. Seti-Merneptah was most likely the same man as king Seti II, whose reign was traditionally thought to have followed upon Amenmesse's reign. The cartouches of Seti II's tomb in Upper Egypt were deliberately erased and then repainted, suggesting that Seti's rule in Upper Egypt was temporarily interrupted by agents of his half-brother. Confusion generally clouds Amenmesse's reign and its correct position within the succession sequence of the rulers of the Egyptian 19th Dynasty. However, an increasing number of Egyptologists today such as Rolf Krauss and Aidan Dodson maintain that Seti II was in fact the immediate successor of Merneptah "without any intervening rule by Amenmesse." Under this scenario, Amenmesse did not succeed Merneptah on the throne of Egypt and was rather a rival king who usurped power sometime during Years 2 to 4 of Seti II's reign in Upper Egypt and Nubia where his authority is monumentally attested. Amenmesse was documented in power at Thebes during his third and fourth year (and perhaps earlier in Nubia) where Seti II's Year 3 and Year 4 are noticeably unaccounted for. The treatment of Amenmesse as a rival king also best explains the pattern of destruction to Seti II's tomb which was initially ransacked and later restored again by Seti II's officials. This implies that the respective reigns of Amenmesse and Seti II were parallel to one another; Seti II must have initially controlled Thebes in his first and second years during which time his tomb was excavated and partly decorated. Then Seti was ousted from power in Upper Egypt by Amenmesse whose agents desecrated Seti II's tomb. Seti would finally defeat his rival Amenmesse and return to Thebes in triumph whereupon he ordered the restoration of his damaged tomb.

Rolf Krauss, followed by Aidan Dodson, suggests that Amenmesse was once a Kushite Viceroy called Messuy. In particular, two representations of Messuy on the temple of Amida allegedly show that a royal uraeus had been added to his brows in a way consistent with other pharaohs such as Horemheb, Merneptah and some of the sons of Rameses III. An inscription at the temple of Amada also calls him "the king's son himself" but this may be merely a figure of speech to emphasize Messuy's high stature as Viceroy under Merneptah. However, Frank Yurco notes that various depictions of Messuy in several Nubian temples were never deliberately defaced by Seti II's agents compared to the damnatio memoriae meted out to all depictions of another Viceroy of Kush, Khaemtir, who had served as Amenmesse's Vizier. This strongly implies that Seti II held no grudge against Messuy, which would be improbable if Messuy was indeed Amenmesse. Yurco also observes that the only objects from Messuy's tomb which identified a Pharaoh all named only Merneptah, Seti II's father, which leads to the conclusion that Messuy died and was buried in his tomb at Aniba, Nubia, during Merneptah's reign, and could not be Amenmesse.

The records of a court case early in the reign of Seti II also throw some light on the matter. Papyrus Salt 124 records that Neferhotep, one of the two chief workmen of the Deir el-Medina necropolis, had been killed during the reign of Amenmesse (the king's name is written as Msy in the document). Neferhotep was replaced by Paneb his adopted son, against whom many crimes were alleged by Neferhotep's brother Amennakhte in a strongly-worded indictment preserved on a papyrus in the British Museum. If Amennakhte's allegations can be trusted, Paneb had stolen stone for the embellishment of his own tomb from that of Seti II in the course of its completion, besides purloining or damaging other property belonging to that monarch. Also he had allegedly tried to kill Neferhotep in spite of having been educated by him, and after the chief workman had been killed by "the enemy" had bribed the vizier Pra'emhab in order to usurp his place. Whatever the truth of these accusations, it is clear that Thebes was going through very troubled times. There are references elsewhere to a "war" that had occurred during these years, but it is obscure to what this word alludes—perhaps to no more than internal disturbances and discontent. Neferhotep had complained of the attacks upon himself to the vizier Amenmose, presumably a predecessor of Pra'emhab, whereupon Amenmose had Paneb punished. Paneb, however, then successfully brought a complaint before 'Mose'/'Msy' whereupon the latter decided to dismiss Amenmose from office. Evidently this 'Mose'/'Msy' was a person of the highest importance who most probably should be identified with king Amenmesse himself.

His mother is known to be Queen Takhat, but who she is exactly is a matter of interpretation complicated by inscriptions being revised by Seti II and Amenmesse. Among her titles are "King's Daughter", which would make her a daughter of Merneptah or Ramesses II or possibly a granddaughter of Ramesses. The name Takhat appears in a list of princesses dated to Year 53 of Ramesses II (Louvre 666). If this is the same Takhat, she would be about the same age as Seti II.

A monument from Karnak, carved while Amenmesse was in control of the area, includes the relief of a woman titled "King's Daughter" and "King's Mother". The monument was reinscribed from 'Mother' to 'Wife'. Another statue of Seti II (Cairo CG1198) bears Seti's name surcharged over someone else's while the names of Takhat were left alone. This suggests that Takhat was married to Seti as well as mother to Amenmesse. Others such as Frank Yurco believe Takhat was wife to Merneptah making the rivals Seti II and Amenmesse half-brothers.

Some assume that Twosret, wife of Seti II, was his sister. Amenmesse's wife was thought to be a woman named Baktwerel since she was buried in the same tomb as Amenmesse, KV10. Three mummies were initially present in this tomb, two women and one man. It is uncertain if any of these remains belong to Amenmesse, Takhat, or Baketwerel. The two females Baketwerel and Takhat could have been buried later. Some people believe that Seti II broke into the tomb and had Amenmesse's remains desecrated since his mummy was never found.

Six quartzite statues originally placed along the axis of the hypostyle hall in the Amun Temple at Karnak are thought to be his, although these were defaced and overwritten with the name of Seti II. One of these statues, with the inscription, "the Great Royal Wife Takhat", lends credence to the argument that a Takhat was Amenmesse's wife. Amenmesse was also responsible for restoring a shrine dating from Thutmose III that stands before a temple at El-Tod.