Airtel Africa plans to use the proceeds to reduce debt and grow its business prior to the IPO. The company has operations in 14 African markets, and is the second largest operator on the continent with around 91 million subscribers.
Airtel Africa's Airtel Money mobile wallet service also has around 11.8 million subscribers across the continent.
Singtel, which owns a 39.5% stake in Bharti Airtel, will invest $250 million in Airtel Africa as part of the US$1.25 billion.
As well as Singtel and Softbank, the investors include Singapore state-owned investment vehicle Temasek Holdings, which owns a majority stake in Singtel, and US private equity firm Warburg Pincus.
Singtel International CEO Arthur Lang said Africa is expected to be the world's fastest growing mobile market, with unique mobile subscribers set to grow to more than 500 million by 2020. The market also has a large unbanked population, with only 25% having access to formal banking services.
“Our investment into Airtel Africa reflects our confidence in the long-term growth potential of Africa with its young and growing population,” he said.
“For many of Airtel Africa's customers, the mobile phone is the key enabler for digital and financial inclusion. As Airtel continues to execute on its transformation strategy to become a leader in data and mobile money in Africa, we believe it is in a strong position to benefit from increasing smartphone penetration and mobile money adoption.”