At the first conference in 2018, President Cyril Ramaphosa set a goal of attracting 1.2 trillion rand of investment over the following five years to create sorely needed jobs and lift the growth rate.
The two previous conferences saw combined investment pledges of more than 660 billion rand, but some of those pledges have been scaled back or put on hold because of the pandemic.
Among the biggest pledges on Wednesday, the New Development Bank of the BRICS group of nations promised 32 billion rand of financing for projects in South Africa, Sasol said it would invest a minimum of 5.4 billion rand and PepsiCo said it would invest 5.5 billion rand.
Ramaphosa said the new commitments were significant given the subdued global economic climate.
Last month, Ramaphosa unveiled a COVID-19 recovery plan focused on public works and job creation.
Unemployment hit a record high during the pandemic, and second-quarter GDP fell more than 17% in annual terms.
Ramaphosa has been trying to restore investor confidence in Africa's most industrialised economy since replacing scandal-plagued Jacob Zuma as head of state in February 2018.
He has promised sweeping reforms in sectors such as energy, but has been constrained by infighting in the governing African National Congress and the weak state of the country's public finances.
The economy is forecast to contract by at least 7% this year because of the pandemic. ($1 = 15.4246 rand)
(Reporting by Alexander Winning; Editing by Alex Richardson)
