The council has led an extensive tendering process via the South West Wales Regional Contractors Framework for firms to deliver the scheme.
Zone One will feature education, business, research, leisure and health facilities to provide social and economic benefits to people in the region.
The council and Bouygues have now entered into an initial pre-construction period ahead of work starting on site next year.
During this period, further design will be undertaken together with preparation and submission of detailed planning information and preparatory works on site.
Property and construction consultants Gleeds will manage the build contract, supported by design and planning experts Arup.
Simon Barnes, Pre-Construction Director for Bouygues UK, said: “We are delighted to have been selected as preferred bidder on the Pentre Awel project, a first of its kind project in Wales. Our experience in large scale projects like this will ensure the successful delivery of the scheme.
“We are pleased that Carmarthenshire County Council is aligned with our ambitious vision to bring a positive social impact alongside this project. Together with our supply chain we look forward to bringing lasting value to the local community.
“Through engagement with regional learning and skills partnerships, we will also help deliver learning and career opportunities. This project will also benefit from using a local supply chain with particular focus on small and medium size enterprises.”
The Pentre Awel project includes integrated care and physical rehabilitation facilities, a well-being skills centre which will focus on health and care training, a clinical delivery centre to deliver multi-disciplinary care, and a new state-of-the-art leisure centre, along with landscaped outdoor public spaces for walking and cycling.
A hotel, a range of social and affordable housing, assisted living accommodation and a nursing home are being planned for later phases of the scheme.