|Millennium:||1st millennium BC|
|75 BC by topic|
|Gregorian calendar||75 BC|
|Ab urbe condita||679|
|Ancient Egypt era||XXXIII dynasty, 249|
|- Pharaoh||Ptolemy XII Auletes, 6|
|Ancient Greek era||176th Olympiad, year 2|
|Balinese saka calendar||N/A|
|Chinese calendar||乙巳年 (Wood Snake)|
2622 or 2562
— to —
丙午年 (Fire Horse)
2623 or 2563
|Coptic calendar||−358 – −357|
|Ethiopian calendar||−82 – −81|
|- Vikram Samvat||−18 – −17|
|- Shaka Samvat||N/A|
|- Kali Yuga||3026–3027|
|Iranian calendar||696 BP – 695 BP|
|Islamic calendar||717 BH – 716 BH|
|Minguo calendar||1986 before ROC|
|Seleucid era||237/238 AG|
|Thai solar calendar||468–469|
52 or −329 or −1101
— to —
53 or −328 or −1100
Year 75 BC was a year of the pre-Julian Roman calendar. At the time it was known as the Year of the Consulship of Octavius and Cotta (or, less frequently, year 679 Ab urbe condita). The denomination 75 BC for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.
- In Rome, the tribune Quintus Opimius speaks out against Sullan restrictions on the tribunate, in orations noted for sarcasm against conservatives.
- Cicero is quaestor in Western Sicily.
- Nicomedes IV of Bithynia bequeaths his kingdom to Rome on his death (75/4 BC). Angered by the arrangement, Mithridates VI of Pontus declares war on Rome and invades Bithynia, Cappadocia and Paphlagonia, thus starting the Third Mithridatic War.
- Third Mithridatic War: M. Aurelius Cotta is defeated by Mithridates in the Battle of Chalcedon.
- Julius Caesar travels to Rhodes to study under Apollonius Molon. On his way across the Aegean Sea, he is kidnapped by Cilician pirates and held prisoner in the Dodecanese islet of Pharmacusa. The young Caesar is held for ransom of twenty talents, he insists they ask for fifty. After his release Caesar raises a fleet at Miletus, pursues and crucifies the pirates in Pergamon.
- Start of Golden Age of Latin Literature.