A last Welsh threat arose when Owain Glyn Dwr was proclaimed Prince of Wales and took up arms against the newly installed Henry IV. In the battle of Bryn Glâs (or Pilleth to the English) in 1402 a large force of English under Edmund Mortimer, consisting mainly of the Herefordshire levy, were heavily defeated by a Welsh army led by Owain. Owain moved on to make his headquarters at Leominster. The defeat caused consternation at Henry IV's court and steps were quickly taken to limit the damage by improving defences at Clifford, Brecon and elsewhere. Tales of the mutilation of corpses by the Welsh added horror to the English accounts of the action. The late 14th century hall of the Hereford Vicars Choral. This was outside the walled precinct of the cathedral. There was always a danger that the clergymen would be mugged on their way to church.

The defeat of Owain's allies Henry Percy (Hotspur) and Douglas at Shrewsbury in July 1403 did not remove the threat further south. On the afternoon of the 3rd September, Richard Kingston, the sometime Dean of Windsor and archdeacon of Hereford, writing at Hereford 'in very great haste' reported that a Welsh force had entered the County. King Henry appeared with an army at Hereford on 11th September. Henry marched into Wales but, lacking the means to supply his army, returned to Hereford in October.

Owain was undefeated and in early August 1405 was joined by a French army, which landed at Milford Haven. The English mustered at Hereford on 29th August but no battle was joined and elements of the Franco-Welsh army seem to have been active in Herefordshire.

When Henry V succeeded to the English throne in March 1415 he wanted an end to the Welsh problem. Henry offered Owain a pardon but no answer was ever received. Glyn Dwr's death is not recorded nor is his burying place, but it is considered a strong possibility that he died at the house of his daughter, Alys Scudamore, at Monnington in the Golden Valley.

On 2nd february1461, during the Wars of the Roses, a Lancastrian force, including Bretons and Frenchmen, was intercepted and defeated by the Yorkist Edward, Earl of March at the Battle of Mortimer's Cross, 25 kilometres north-west of Hereford. One of the Lancastrian leaders, Owen Tudor, was captured and taken into Hereford. Owen was a high-ranking nobleman - he had married Catherine of France, the widow of Henry V.