During the consulship with Antonius Hybrida, who learned of a conspiracy to overthrow the republic in 63 B.C.?

The person who learned of the conspiracy to overthrow the republic in 63 B.C. was Marcus Tullius Cicero. During his consulship, he received reports about a plot led by Lucius Sergius Catilina, commonly known as Catiline, to assassinate several senators and seize power. Cicero, recognizing the gravity of the conspiracy, took decisive action by calling the Senate into session and revealing the details of the conspiracy in a series of speeches known as the Catiline Orations. His efforts to thwart Catiline’s plans are celebrated as a crucial moment in the defense of the Roman Republic.

Cicero's background as a lawyer and orator played a significant role in shaping his approach to the conspiracy; he used his skills to rally public opinion against Catiline and ultimately ensured that the conspirators were arrested and executed. His actions not only preserved the Republic at that time but also solidified his reputation as a significant political figure in Roman history.