The flagship brand of South African Breweries (SAB) will feature on the sleeve of the Proteas' playing kit for the final in the longest format.
Commenting on the sponsorship, CSA chief executive officer, Pholetsi Moseki, said: "CSA is pleased to welcome Castle Lager as the official team sponsor for the ICC World Test Championship Final.
"The show of support for the Proteas Men reaffirms Castle Lager's long-standing and consistent support of South African cricket.
"We are humbled to go into the WTC Final with a brand that reflects a shared belief in the power of unity, resilience, and national pride.
"Castle Lager's backing serves as a rallying cry to the nation to stand behind our boys as they chase Test cricket greatness on the global stage."
Castle Brand director, Thomas Lawrence, said: "Castle Lager is proud to be back on the Proteas Test jersey - a symbol of resilience, pride, and South African excellence.
"Our return marks not just a sponsorship, but a renewed commitment to the spirit of Test cricket and the values it shares with our brand: heritage, endurance, and unity.
"Together with the Proteas, we look forward to writing the next great chapter in South African cricket."
The Proteas Test squad will assemble in Arundel, Sussex on 31 May and will play a warm-up match against Zimbabwe from 3 June, before heading to London on 7 June.
Simon Harmer says it is privilege to represent the Proteas after scooping the ICC Player of the Month award for November following his heroics in the historic Test series win in India.
In a tough afternoon for the batters, the Proteas were bowled out for 117 and suffered a seven-wicket defeat to India in the third T20I of their tour to India.
South Africa produced a ruthless all-round display to beat India by 51 runs in the second T20I of the five-match series at New Chandigarh on Thursday, taking firm control of the tour.
Hardik Pandya struck forceful half-century and then took a wicket as India crushed the Proteas by 101 runs in the first of five T20Is played in Cuttack on Tuesday.
