Rugby Union side Llanelli Scarlets announced the deal with Castell Howell Foods, which sees the family-owned business advertising on the south stand of the new Parc y Scarlets after being a sleeve sponsors last season.
Gareth Davies, Llanelli Scarlets managing director, said: "We have retained a great partnership with Castell Howell Foods over many years and this major sponsorship is a huge step forward and cements our connection with the highly successful Carmarthenshire-based business."
The new stadium holds a capacity of 15,000 compared to the 10,800 of its previous home at Stradey Park. Davies added: "We are very grateful for the company's continued support of our region."
The Scarlets play against Scottish, Welsh and Irish teams in the Magners League and finished sixth last season. Castell Howell Foods director Kathryn Jones said: "We are delighted and very proud to be a main sponsor of the new Parc y Scarlets stadium and to continue our support of the Llanelli Scarlets in this new chapter in the region's history."
The Carmarthenshire firm has been in operation since the mid-198Os. Its products include cooked ham and Welsh beef and lamb. "The Scarlets are a major name and force within this area and we look forward to a successful partnership over the next five years with one of the most celebrated and high-profile rugby regions in Wales," added Jones.
"This is a very impressive new stadium in Llanelli, which will not only boost the Scarlets as they go forward, but will also benefit a wide-range of people and sports clubs in the area, thanks to the associated community facilities."
The new stadium is hoped to be completed by mid-November and the first home match at the ground will be against Munster on 28 November.