After a short power struggle with her mother, Berenice married her half-cousin Ptolemy III, the third ruler of the Ptolemaic kingdom.

As queen of Egypt, Berenice participated actively in government, was incorporated into the Ptolemaic state cult alongside her husband and worshipped as a goddess in her own right.

[15] Control of Cyrene was then entrusted to a republican government, led by two Cyrenaeans named Ecdelus and Demophanes, until Berenice's actual wedding to Ptolemy III in 246 BCE after his accession to the throne.

[16] This brought Cyrenaica back into the Ptolemaic realm, where it would remain until her great-great-grandson Ptolemy Apion left it to the Roman Republic in his will in 96 BCE.

In 244 or 243 BCE, Berenice and her husband were incorporated into the Ptolemaic state cults and worshipped as the Theoi Euergetai (Benefactor Gods), alongside Alexander the Great and the earlier Ptolemies.

[21] This cult closely parallels that offered to her mother-in-law, Arsinoe II, who was also equated with Aphrodite and Isis, and associated with protection from shipwrecks.

According to this story, Berenice vowed to sacrifice her long hair as a votive offering if Ptolemy III returned safely from battle during the Third Syrian War.

Conon of Samos, the court astronomer identified a constellation as the missing hair, claiming that Aphrodite had placed it in the sky as an acknowledgement of Berenice's sacrifice.

[26][21] The poet Callimachus, who was based in the Ptolemaic court, celebrated the event in a poem, The Lock of Berenice, of which only a few lines remain.

[27] The first century BCE Roman poet Catullus produced a loose translation or adaptation of the poem in Latin,[28] and a prose summary appears in Hyginus' De astronomia.

[29][21] When she won in the four-horse chariot race at the Olympics in the early third century BCE, she commissioned an epigram by the poet Posidippus in which she explicitly claimed to have "stolen" the fame (κῦδος) of Cynisca.

By 211 BCE, she had her own priestess, the athlophorus ('prize-bearer'), who marched in processions in Alexandria behind the priest of Alexander the Great and the Ptolemies, and the canephorus of the deified Arsinoe II.