While no financial details of the three-year deal were announced at a function, AFP understands it is worth about 20 million rand ($1.5 million/1.3 million euros) annually.
First National Bank — one of the four largest in South Africa — will have their name and logo on the back of the famed green and gold shirt between the collar and the team number.
It is the second recent boost for the national rugby body, which posted a 23.3 million rand loss last year.
South Africa-based international telecommunications company MTN became the front-of-shirt Springbok sponsor this year, reportedly for 50 million rand a year.
Absa, another of the major banks, abandoned their 90 million rand-a-year role as sole Springbok shirt sponsors last year.
The bank was reportedly unhappy with negative publicity SA Rugby attracted over slow racial transformation of the previously white-dominated sport.
Blacks, who comprise more than 90 percent of the population, were barred from playing for the Springboks for most of the apartheid era.
Government unhappiness with the pace of racial change led to SA Rugby being barred last year from bidding to host international tournaments.
This ban was recently lifted, allowing South Africa to compete with France and Ireland for the right to host the 2023 Rugby World Cup with a decision due on November 15.