For most of its history, the Carmarthenshire constituency was dominated by a small number of powerful families. Chief among these were the Rice family of Dynevor, who could claim descent from the medieval Lord Rhys of Deheubarth. They drew upon traditional loyaltiy and the connotations linked to the Dynevor name to maintain their status as the leading political family of the county and leaders of the Red or Tory faction.
In 1790 the influence of the Dynevor family was re-asserted when George Talbot Rice was elected unopposed. Four years later, he was elevated to the House of Lords and the family would not be in a position to represent the county again until 1820 when his yet unborn son would have came of age.
A celebrated contest took place in 1802 between James Hamlyn Williams and William Paxton. The contest was said to have cost Paxton a total of £15,000. This included 11,070 breakfasts, 36,901 dinners, 25,275 gallons of ale, 11,068 bottles of spirits, 8,879 bottles of porter, 460 of sherry, 509 of cider and gallons of milk punch. The contest became known as ‘Lecsiwn Fawr’ (the Great Election). Paxton was defeated and spent two years settling his debts.
In 1820, George Rice Trevor was elected MP for Carmarthenshire and held the seat until 1831. Following the Great Reform Act, the county was awarded a second seat. In 1832, Rice Trevor resumed his seat and served until 1852 when he was elevated to the House of Lords upon inheriting the title of Lord Dynevor.
Representation continued to be dominated by Conservative landowners such as David Jones of Pantglas, who served from 1852 until 1868. However, David Pugh, member from 1857 was regarded as a Liberal-Conservative, who in later life migrated to the Liberal Party.
At the 1868 General Election, following a lengthy and lively campaign characterized by accusations of coercion, Edward Sartoris captured a seat for the Liberals. He was defeated in 1874 but in 1880 the Liberals again captured a seat. Following the Third Reform Act the constituency was divided into two single-member seats.
^The Dictionary of National Biography records Mansell as MP for Carmarthen borough in the 1604 Parliament and for the county only in 1614, but Cobbett's Parliamentary History names Mansell as MP for the county in 1604 and Sir Walter Rice as the borough MP