Barclays has completed a near 30 billion rand (£2.6bn; $4.5bn) purchase of a 54% stake in South Africa's largest retail lender Absa.
Barclays secured the deal after an eight-month courtship
"Today is the day that we begin to combine our resources and skills to create the pre-eminent bank on the African continent," Absa's chief said.
Barclays said the transaction was the largest ever foreign direct investment in South Africa.
"Absa is a valuable addition to the Barclays Group," the bank added.
Absa has more than 30,000 employees, seven million customers and 670 outlets. It is also South Africa's largest internet bank.
Following the deal four Barclays executives are to join Absa's executive committee.
The purchase of the majority stake in Absa is Barclays' largest investment outside the UK.
The UK bank withdrew from South Africa in 1986 following pressure from anti-apartheid protesters.