Glyndŵr was born around 1349 (possibly 1359) to a prosperous landed family, part of the Anglo-Welsh gentry of the Welsh Marches (the border between England and Wales) in northeast Wales.
Glyndŵr was a descendant of the Princes of Powys through his father Gruffydd Fychan II, hereditary Tywysog of Powys Fadog and Lord of Glyndyfrdwy, and of those of Deheubarth through his mother Elen ferch Tomas ap Llywelyn ab Owen.
After inheriting estates in Merioneth, Glendower probably studied law at one of the Inns of Court in London.
By 1385 he was serving as a squire with King Richard II against the Scots.
Possibly knighted in 1387, he also served the Earl of Arundel under Henry of Lancaster (who became Henry IV in 1399).
Glendower headed a Welsh rebellion in 1399, and, after being captured at Flint Castle, he was pardoned, but some of his lands were not restored to him.
He and his followers seized south Wales and gained control of Conway, Ruthin, and Hawarden; they also attacked the royal army in the north.
In 1402 Glendower was crowned at Machynlleth, and he simultaneously negotiated with the English for peace and with Ireland and Scotland for help.
This alliance ended with the Battle of Shrewsbury (1403), in which Glendower failed to join the Percys.
Capturing Harlech and Cardiff, Glendower controlled the area west of Worcester, and in 1405 he called for a Welsh Parliament. From 1405 onward, Glendower's power started to decline, and his sons were captured by Prince Henry.
Glendower recaptured Carmarthen with the help of the French, but he was defeated in battle in 1406, deserted by his ally the Earl of Northumberland the following year, and then lost Aberystwyth in 1408 and south Wales.
Owain married Margaret Hanmer, also known by her Welsh name Marred ferch Dafydd, daughter of Sir David Hanmer of Hanmer, early in his life. Owain's daughter Alys had secretly married Sir John Scudamore, the King's appointed Sheriff of Herefordshire. A grandchild of the Scudamores was Sir John Donne of Kidwelly, a successful Yorkist courtier, diplomat and soldier. Glendower's wife and several of his relatives were captured by the English in 1413.
