Pharnaces I (lived 2nd century BCE), fifth king of Pontus, is of Persian and Greek Macedonian ancestry.

He is the son of King Mithridates III of Pontus and his wife Laodice, whom he succeeds on the throne.

Pharnaces has two siblings: a brother called Mithridates IV of Pontus and a sister called Laodice who succeed as Pontian monarchs on the throne.

He is born and raised in the Kingdom of Pontus.