Thomas Horton was a strong opponent of Charles I and joined the Parliamentary forces after the outbreak of the Civil War. He served under Arthur Haselrig and eventually rose to the rank of colonel in the New Model Army.
In December 1647, Parliament declared that all soldiers who had enlisted after 6th August, 1647 were to be dismissed without pay. Those that had joined at an earlier stage of the war were to receive only two months wages.
John Poyer, the military governor of Pembroke, was furious when he heard the news and began making speeches to his soldiers attacking Parliament's decision to disband the army. Other soldiers based in South Wales, who had heard about Poyer's actions, began to head for Pembroke to give him their assistance. John Poyer's supporters included the two most senior army officers in South Wales, Major-General Rowland Laugharne and Colonel Rice Powell.
When Parliament heard about Poyer's actions in Pembroke they sent Horton with 3,000 troops to deal with the rebellion. Rowland Laugharne and nearly 8,000 rebels left Pembroke and engaged Horton's parliamentary army at St. Fagans in Glamorgan. Although outnumbered, Horton's experienced and well-disciplined army was able to defeat Laugharne's poorly armed soldiers. Over 200 of Laugharne's men were killed and another 3,000 were taken prisoner. Laugharne and what was left of his army, managed to escape back to Pembroke.
Thomas Horton died while serving with Oliver Cromwell during the the Irish campaign in 1650.
A few men... have already gotten too much power into their hands, and want to disband us... So they can enslave the people... and establish taxes. We promise to protect the people from injury and maintain the Protestant religion... as established by the law in this land. We therefore crave the assistance of the whole kingdom.
As commander of these counties... I cannot ignore the affronts put upon my men... Instead of receiving their pay allowed them by Parliament... they have been disbanded... This happened in my absence, and to my knowledge, still unrighted... I believe that my past service for your country... merited much better treatment.
On Monday morning... the enemy advanced towards us... we took the best ground... About sixty men on horses charged once, but we beat them back, and after that none of the men on horses appeared again... The enemy tell us they were 8,000. We had a sharp dispute with them for about two hours. Our men on horses charged the enemy, who were wholly routed... Many of the enemy were slain... We have taken 3,000 prisoners... we have not lost many soldiers and not one of our officers.