Riverstone Holdings, where Lord Browne is a partner, will float investment company Riverstone Energy in late October and will use the proceeds to invest across the global energy market.
Lord Browne will be on the board of the new investment company, alongside a number of senior industry figures, including Sir Robert Wilson, former chairman of BG Group, and Jim Hackett, former chief executive of Anadarko Petroleum.
Brunswick previously worked with Lord Browne at BP, with founder Alan Parker personally advising Browne during his resignation from the oil giant after the publication of details concerning his personal life.
Brunswick partners Andrew Mitchell and Robin Wrench are handling comms around the IPO.
The listing is one of a number of significant IPOs announced this month, notably the mega-floats of Twitter in the US and Royal Mail in the UK.
Brunswick is handling corporate PR for the Royal Mail float alongside Tulchan Communications, which is handling investor relations.
Figures recently published by the Financial Times suggest that 2013 could be the best year for new listings since the financial crisis began and 2014 will be better still.
The FT found that the domestic new listings market has reached £1.8bn in the first half of the year, with the recently announced flotations suggesting the full-year total could reach £7.8bn (the second highest total since 2007).