According to reports, Mainstream Capital aims to "target" insurance companies and pension funds for as much as EUR 3 billion.
At the launch of venture, Mainstream CEO Eddie O'Connor said he believed the development of the company's own capital-raising arm would help finance projects at an early stage.
O'Connor said: "We have built a credible business. When you get this big, there is an exercise in corporate branding in the sense that people know that we know what we're doing. We have a great track record and our projects allow pension funds and insurance companies to take a sensible outlook over a 20-year period."
The announcement follows a number of partnership and investment deals for the company over the last year.
Japanese trading company Marubeni completed a EUR 100 million investment in Mainstream in October to further finance its move into emerging markets.
Speaking at the time about the Actis deal, Mainstream chief executive Eddie O'Connor said Mainstream could look to replicate it, with or without Actis, in other markets.