Stocks ended higher, helping the main index bounce back from its lowest level in nearly 10 months with Steinhoff in demand after the retailer lifted its quarterly operating profit.
By 15:30 GMT the rand had gained 1.33% to 13.4875 per dollar, breaking through the crucial technical barrier of 13.5000 that traders said could see the unit strengthen even further.
The rand brought its gains against the greenback to more than 4% since last Friday's decision by S&P Global Ratings to keep the country's credit score at investment level.
"The expectation that the ECB will announce an expansion of its asset purchasing programme should support demand for the currency," ETM Analytics market analyst Ricardo da Camara said.
The rand was also soothed by a report on Wednesday that business confidence had risen to its highest in four months in November.
Da Camara said third-quarter current account figures, due for release on Friday by the central bank, would determine whether the rand could hold on to recent gains.
"For the markets, longer term, it will give an indication on how the country will be able to finance the budget deficit," he said.
On the bourse the blue-chip JSE Top-40 index advanced 1.2% to 42,927 and the broader All-share index added 1.1% to 49,476.
