Year 635 (DCXXXV) was a common year starting on Sunday (link will display the full calendar) of the Julian calendar. The denomination 635 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.
|Ab urbe condita||1388|
|Balinese saka calendar||556–557|
|Chinese calendar||甲午年 (Wood Horse)|
3331 or 3271
— to —
乙未年 (Wood Goat)
3332 or 3272
|- Vikram Samvat||691–692|
|- Shaka Samvat||556–557|
|- Kali Yuga||3735–3736|
|Minguo calendar||1277 before ROC|
|Seleucid era||946/947 AG|
|Thai solar calendar||1177–1178|
761 or 380 or −392
— to —
762 or 381 or −391
- Emperor Heraclius makes an alliance with Kubrat, ruler (khagan) of Great Bulgaria, to break the power of the Avars on the Balkan Peninsula.
- Judicaël, high king of Domnonée (Brittany), visits King Dagobert I at his palace in Clichy (northwest of Paris), to promise he will remain under Frankish lordship. The Breton king arrives with gifts, but insults Dagobert by refusing to eat at the royal table.
- King Meurig of Glywysing and Gwent invades Ergyng (Archenfield), and reunites the two Welsh kingdoms (approximate date).
- King Gartnait III dies after a 4-year reign, and is succeeded by his brother Bridei II, as ruler of the Picts.
- January – Battle of Fahl: The Rashidun army, (30,000 men) under Khalid ibn al-Walid (known as the "Drawn Sword of God"), defeats the Byzantine forces led by Theodore Trithyrius, at Pella in the Jordan Valley (Jordan).
- Gaza is conquered by the Muslim Arabs under 'Amr ibn al-'As. It becomes the first city in Palestine developed into a centre of Islamic law.
- Yao Silian, Chinese historian, completes his Book of Liang. It contains the history of the Liang Dynasty.
- Christian missionaries arrive in China: Alopen, bishop of the Assyrian Church of the East, preaches Nestorian Christianity to the Tang Dynasty.
- Aidan of Lindisfarne, Irish missionary, founds the monastery of Lindisfarne in Northumbria (Northern England).
- Birinus, Frankish missionary, converts King Cynegils of Wessex and becomes the first Bishop of Dorchester.
- Smith, Julia M. H. (1992). Province and Empire: Brittany and the Carolingians. Cambridge University Press. pp. 19, 21. ISBN 978-0-521-03030-4.