An election to the Carmarthenshire County Council was held in April 1958.^[1] It was preceded by the 1955 election and followed, by the 1961 election.

A close run election resulted in Labour narrowly regaining control of the authority. The Carmarthen Journal bemoaned the lack of organization amongst the Independents, compared with Labour and referred to the haphazard methods of nomination, particularly in rural areas.^[2] Labour took all nine aldermanic vacancies.^[3]

There were no boundary changes at this election.

A number of retiring councilors stood down to allow retiring aldermen to be returned unopposed. These included a Plaid Cymru councilor at Ammanford in favour of retiring Labour alderman, John Harries.^[4]

There were more unopposed returns than in any previous election, according to one local newspaper.^[2] In Llanelli, where many wards had been closely contested at previous county elections, Labour candidates were returned unopposed in all nine divisions. These included the No.1 Ward which had been held by an Independent in the previous council.

In the few contests that took place very few seats changed hands. In Carmarthen, an Independent councilor was defeated by a Ratepayer candidate.

59 councillors were elected.

In addition to the 59 councillors the council consisted of 19 county aldermen. Aldermen were elected by the council, and served a six-year term. Following the elections, the majority of the aldermanic vacancies were taken by Labour.

Following the selection of aldermen the following by-elections were held.^[5]