The rand traded 0.6% firmer at 14.8450 per dollar at 1530 GMT.
The Top-40 stock index closed 1.55% lower at 49,559 points while the broader all-share was down 1.39% at 55,622 points.
However, bucking the declines were mining shares, led by gold miners as price of bullion rose.
Shares in Sibanye-Stillwater jumped 5.68%, Gold Fields shares rose 4.39%, while AngloGold Ashanti was up 3.18%.
The yield on the benchmark 2026 government bond dipped 1 basis point to 8.285%.
Peregrine Treasury Solutions said in a note that while the rand had firmed from a session low touched earlier, it had still started the week on the "backfoot" as investors waited for more clarity over the US-China talks.
Although Washington and Beijing labelled two days of talks last week as "productive" and "constructive", a deal appeared elusive after Chinese officials unexpectedly cancelled a visit to farms in the US on Friday.
Weaker-than-expected global economic data added to investor worries over the trade dispute's effects on the world economy.
"Despite some perceived progress in US-China trade negotiations, markets remain hesitant on this front given the stop-start nature of the evolving trade discussions, while Brexit too does not have a clear outcome yet," said Investec chief economist Annabel Bishop.
"The rand is likely to remain volatile, with September a month that can see a lot of churn, and with the risk that slower global growth sees commodity currencies such as the rand weaken further."