The 24-year old becomes Welsh-qualified at the end of the season and boosts Scarlets ahead of their the European Rugby Champions Cup campaign.
We're delighted to be welcoming Rynier to Scarlets for the season," said general manager Jon Daniels.
"I'm looking forward to continuing my development with the Scarlets," said Bernardo.
I have met with Wayne and Jon a couple of times and have been impressed with the culture and ambition at the Scarlets.
I hope to make an impression and help the region fight for silverware and to be competitive as the only Welsh region in Europe."
Bernardo is a product of Eastern Province Kings and made 10 Super Rugby appearances for Port Elizabeth based Southern Kings in Super Rugby.
South African lock Rynier Bernardo has joined Scarlets from Pro 12 rivals Ospreys.