The former India captain won a bidding war against former New Zealand skipper Stephen Fleming, who wanted Brevis for rival SA20 franchise Joburg Super Kings.
The price paid for Brevis eclipsed the record of R14-million (US$798,000) which took South African T20 international captain Aiden Markram to Durban Super Giants just minutes earlier.
Markram was the first player to breach the R10-million barrier for the tournament, which will be played from December 26 to January 25.
Ganguly said he hoped home-town player Brevis' six-hitting would be suited to the Capitals' home ground at Centurion, known as a high-scoring venue.
"He's a tremendous talent," said Ganguly. "He's really gone forward in the last one-and-a-half years. He's a game changer and that's what you need in T20 cricket."
Brevis went to the same school as South African star AB de Villiers and early in his career was nicknamed 'Baby AB' for the similarities in their playing styles.
After scoring only five in his first two T20I innings in 2023, Brevis, 22, returned in July.
He made a South African T20 international record 125 not out against Australia in Darwin last month, an innings that included eight sixes.
He has hit 313 in eight innings since his return, at an average of 52.16.
South African players attracted the biggest bids in the auction.
Wiaan Mulder, Matthew Breetzke, Rassie van der Dussen, Nandre Burger, Anrich Nortje, Gerald Coetzee and Ottneil Baartman all sold for R5-million or more.
Several overseas players went unsold but fast bowlers Australia's Dan Worrall (Joburg Super Kings) and England's Saqib Mahmood (Pretoria Capitals) both fetched R1.5-million.
England's Craig Overton went to the Pretoria team for R1-million.
Veteran former England bowler James Anderson, 43, was up for auction at a base price of R1-million but attracted no bids.
South Africa's World Test Championship winning captain Temba Bavuma went unsold at the minimum base price of R200,000.