The lender was a part of Banco Portugues de Negocios, which was nationalised in the financial crash in 2008.
Cabot Square paid €36m (£28.5m) in an initial investment, taking on a firm with an asset book over more than €200m. BPN Credito specialises in car finance, and also runs leasing operations for equipment.
The purchase comes at a difficult time for the Portuguese finance sector. Even several years on from the crash, it is still reeling from bad pre-crisis loans.
In the summer, Banco Espirito Santo collapsed, and regulators stepped in the resolve the lender.
“Portuguese consumers have seen their credit options reduced sharply since the credit crunch,” said Cabot Square’s Tarun Sharma.
“With the economy showing an improvement, the Portuguese consumer credit market represents an opportunity for growth.”