The Series C fund-raising was likely to value the company at more than $500 million on a pre-money basis, Sky News said, citing sources.
PrimaryBid's latest capital-raising will take the total sum it has raised since it was founded in 2016 to more than $200 million, the report said.
The funding from Softbank's Vision Fund II will provide PrimaryBid with "greater financial firepower" to continue its expansion beyond the UK, Sky News said.
SoftBank and PrimaryBid were not immediately available for comment outside business hours.
(Reporting by Rhea Binoy in Bengaluru; Editing by Toby Chopra)