She is recorded in Manetho's Epitome as a certain Thuoris, who in Homer is called Polybus, husband of Alcandra, and in whose time Troy was taken. She was said to have ruled Egypt for seven years, but this figure included the nearly six-year reign of Siptah, her predecessor. Twosret simply assumed Siptah's regnal years as her own. While her sole independent reign would have lasted for perhaps one to one and a half years from 1191 to 1189 BC, this number now appears more likely to be two full years instead, possibly longer. Excavation work by the University of Arizona Egyptian Expedition  on her memorial temple ("temple of millions of years") at Gournah strongly suggests that it was completed and functional during her reign and that Twosret started a regnal year 9, which means that she had two and possibly three independent years of rule, once one deducts the nearly six-year reign of Siptah. Her royal name, Sitre Meryamun, means "Daughter of Re, beloved of Amun."
Twosret or Tausret's birth date is unknown. Twosret is thought to have been a daughter of Merenptah, possibly a daughter of Takhat, thereby making her sister to Amenmesse. She was thought to be the second royal wife of Seti II. There are no children for Twosret and Seti II, unless tomb KV56 represents the burial of their daughter.
Theodore Davis identified Twosret and her husband in a cache of jewelry found in tomb KV56 in the Valley of the Kings. This tomb also contained objects bearing the name of Rameses II. There is no consensus about the nature of this tomb. Some (Aldred) thought this was the tomb of a daughter of Seti II and Tawosret, but others (Maspero) thought this was a cache of objects originally belonging with the tomb of Tawosret herself.
After her husband's death, she became first regent to Seti's heir Siptah jointly with Chancellor Bay. Siptah was likely a stepson of Twosret since his mother is now known to be a certain Sutailja or Shoteraja from Louvre Relief E 26901. When Siptah died, Twosret officially assumed the throne for herself, as the "Daughter of Re, Lady of Ta-merit, Twosret of Mut", and assumed the role of a Pharaoh.
While it was commonly believed that she ruled Egypt with the aid of Chancellor Bay, a recently published document by Pierre Grandet in a BIFAO 100 (2000) paper shows that Bay was executed on Siptah's orders during Year 5 of this king's reign. The document is a hieratic ostracon or inscribed potshard and contains an announcement to the workmen of Deir El-Medina of the king's actions. No immediate reason was given to show what caused Siptah to turn against "the great enemy Bay," as the ostracon states. The recto of the document reads thus:
This date accords well with Bay's last known public appearance in Year 4 of Siptah. The ostracon's information was essentially a royal order for the workmen to stop all further work on Bay's tomb since the latter had now been deemed a traitor to the state.
Meanwhile, Egyptian territories in Canaan seem to have become effectively independent under the overlordship of a man called Irsu. Papyrus Harris I, the main source on these events, seems to claim that Irsu and Twosret had allied themselves, leaving Irsu free to plunder and neglect the land.
Twosret's reign ended in a civil war, which is documented in the Elephantine stela of her successor Setnakhte, who became the founder of the Twentieth dynasty. It is not known if she was overthrown by Setnakhte or whether she died peacefully in her own reign; if the latter is the case, then a struggle may have ensued among various factions at court for the throne in which Setnakhte emerged victorious. However, Setnakhte and his son Ramesses III described the late 19th dynasty as a time of chaos. Setnakhte usurped the joint KV14 tomb of Seti II and Twosret but reburied Seti II in tomb KV15, while deliberately replastering and redrawing all images of Twosret in tomb KV14 with those of himself. Setnakhte's decisions here may demonstrate his dislike and presumably hatred for Twosret since he chose to reinter Seti II but not Twosret.
Setnakhte's son, Ramesses III, later excluded Twosret and even Siptah of the 19th dynasty from his Medinet Habu list of Egyptian kings thereby delegitimizing them in the eyes of the citizenry. It appears more likely that Setnakhte overthrew Twosret from power in a civil war.
Twosret's highest known date is a Year 8 II Shemu day 29 hieratic inscription found on one of the foundation blocks (FB 2) of her mortuary temple at Gournah in 2011 by the University of Arizona Egyptian Expedition. Since this was only a foundation inscription and Twosret's temple, although never finished as planned, was at least partially completed, it is logical to assume that some time must have passed before her downfall and the termination of work on her temple project. Richard Wilkinson stressed that Twosret's mortuary temple was "largely structurally completed," although bearing minimal decoration; therefore, she would have ruled for several more months beyond II Shemu 29 of her 8th Year for her temple to reach completion. Further study by Pearce Paul Creasman has concluded that the temple was "functionally complete."  She could, hence, have possibly ruled for 6 to 20 more months after the inscription date to achieve these levels of completion, thus starting her 9th regnal year around the interval of IV Akhet/I Peret--when her husband died (since she assumed Siptah's reign as her own) or perhaps longer--before Setnakhte's rule began. Or she could have had a nearly full 9th year reign, including the 6-year reign of Siptah.
It is believed that expeditions were conducted during her reign to the turquoise mines in Sinai and in Palestine and statues have been found of her at Heliopolis and Thebes. Her name is also found at Abydos, Hermopolis, Memphis, and in Nubia.
Inscriptions with Twosret's name appear in several locations:
Twosret's KV14 tomb in the Valley of the Kings has a complicated history; it was started in the reign of Seti II. Scenes show Tawosret accompanying Siptah, but Siptah's name had later been replaced by that of Seti II. The tomb was then usurped by Setnakht, and extended to become the deepest royal tomb in the valley while Tawosret's sarcophagus was reused by Amenherkhepeshef in KV13. Altenmuller believes that Seti II was buried in one of the rooms in KV14 and later reburied in KV15. Others question this scenario.
A mummy found in KV35 and known as Unknown Woman D has been identified by some scholars as possibly belonging to Twosret, but there is no other evidence for this other than the correct Nineteenth Dynasty period of mummification.