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.