Pharnaces II (in Greek Φαρνάκης, died 47 BC) was the son of the great Mithridates VI of Pontus, a famed enemy of the Roman republic.

He was raised as his father's successor and treated with distinction. However, we know little of his youth from writers of the time and find him first mentioned after Mithridates had taken refuge from the Roman general Pompey during the Third Mithridatic War.

Mithridates was keen to wage war with the Romans once more, but his son was less keen, and thus began a plot to remove his father from power. Unfortunately, his plans were discovered, but the army, not wishing to engage Pompey and the Roman armies, supported Pharnaces. They marched on Mithridates and forced their former king to take his own life.

Pharnaces quickly sent an embassy to Pompey with offers of submission and hostages, for he was keen to secure his position. He also sent the body of his father, to be at the disposal of Pompey. The latter readily accepted Pharnaces overtures, for he wished to be back at Rome having seen to have made peace in the region. Pompey granted Pharnaces the Bosporan Kingdom, and named him friend and ally of Rome.

Contemporary historians are silent on Pharnaces's early reign, but eventually, on viewing the increasing power struggles between the Romans, and with an eye to recreating the kingdom of his father, he attacked and subjugated the free city of Phanagoria, violating one of his agreements with Pompey.

In 49 civil war broke out between Julius Caesar and Pompey. Whilst the Romans were distracted by this, Pharnaces decided to seize the opportunity and, with the forces under his disposal and against little opposition, made himself the ruler of Colchis and Lesser Armenia. Deiotarus, the king of Lesser Armenia appealed to Domitius Calvinus, the lieutenant of Caesar in Asia, for support, and soon the Roman forces sought battle with Pharnaces. They met at Nicopolis in Anatolia, and Pharnaces so defeated the Romans that he was easily able to use his army to overwhelm Pontus. He also took the city of Amisus the late city of Pontus (under his father's rule), sold the inhabitants to slave traders and made all the boys eunuchs.

After this show of strength against the Romans, Pharnaces drew back to suppress revolt in his new conquests. However, the extremely rapid approach of Caesar in person forced Pharnaces to turn his attention back to the Romans. At first, recognizing the threat, he made offers of submission, with the sole object of gaining time until Caesars attention fell elsewhere; but Caesar's speed brought war quickly, and battle took place near Zela (modern Zile in Turkey), where Pharnaces was routed and was able to escape with just a small detachment of cavalry. Caesar himself, in a letter to a friend in Rome, famously said of the short war:“Veni, vidi, vici” (“I came, I saw, I conquered”).

Pharnaces himself fled quickly back to the Bosporus, where he managed to assemble a small force of Scythian and Sarmatian troops, with which he was able to gain control of a few cities. However, a former governor of his, Asandar, attacked his forces and killed him. The historian Appian states that he died in battle; Dio Cassius says he was captured and then killed.

Pharnaces was about fifty years old when he died, and he had reigned for nearly sixteen years. He had several sons, one of whom, Dareius, Mark Antony made, for a short while, the king of Pontus. His daughter Dynamis was married to Polemon I, the king of the Bosporus.

This article is partly based on extracts from the book Dictionary of Greek and Roman Antiquities, edited by William Smith (published in 1870), and the writings of Appian, ancient historian.