The company, which has a portfolio of infrastructure assets in the transport, healthcare, education, justice and other services sectors, said the number of shares to be issued and price per share will be determined after the close of a book-build on June 20.
The placing will be available to qualifying new and existing investors and will be launched on Tuesday.
BBGI has been using its existing revolving credit facility to fund recent acquisitions and net debt stands at £57mln.
In recent weeks, it has bought additional interests in the Ohio River Bridges East End Crossing and the A1/A6 public-private infrastructure road project for £58mln.
The group said the proceeds of the equity raise will be used to cut debt and provide it with “additional financial flexibility to pursue primary and secondary investment opportunities”.
Jefferies and Stifel are acting as joint bookrunners for the placing.
Since listing in London in 2011, BBGI’s portfolio has grown from 19 assets to 48 assets.
It was promoted to the FTSE 250 index in October 2018, with its shares having risen nearly 52% since its initial public offering to 158p per share today, representing a market capitalisation of £920.7mln.