Following the death of his older brother Ptolemy XIII of Egypt on January 13, 47 BC, and according to his will, he was proclaimed Pharaoh and co-ruler by their older sister and remaining Pharaoh, Cleopatra VII of Egypt. He was about 12 years old when he acceded to the throne. He and his older sister, Cleopatra, were married, but Cleopatra continued to act as lover of Roman dictator Julius Caesar. Ptolemy is considered to have reigned in name only, as a concession to Egyptian tradition, with Cleopatra keeping actual authority.
On 15 March 44 BC Caesar was murdered in Rome by a group of conspirators whose most notable members were Brutus and Cassius. Ptolemy soon followed him in death. An inscription mentioning him as alive was dated at 26 July 44 BC. It has been assumed but remains uncertain that Cleopatra poisoned her co-ruler, with aconite, to replace him with his nephew Ptolemy XV Caesar, her son by Caesar who was proclaimed co-ruler on 2 September 44 BC and whom his mother intended to support as successor of his father.