The radio group, which has a 4.5% share of the commercial radio market and also owns five regional stations under the Real brand, has long been the subject of takeover rumours and was said to have attracted several offers.
The value of the deal is undisclosed but several reports, including former sister brand The Guardian, have it at £50m.
The stations join the Capital and Heart networks as well as Classic FM in Global’s portfolio.
As a consequence of the deal, GMG Radio CEO Stuart Taylor is to leave the company with immediate effect. He will be replaced by Global’s regional MD Mark Lee.
Ashley Tabor, founder and executive president of Global, says: “We believe that this is a very strong business with brands and assets that are highly complementary to those of Global Radio.”
GMG is reportedly set to announce £45m losses for the year to 31 March. The deficit could lead to compulsory redundancies, according to a weekend report in The Sunday Times.
Andrew Miller, chief executive of GMG: “Our portfolio of investments that lie outside our core national newspaper business exist to underpin the long-term financial and editorial integrity of the Guardian. If we believe that best value for the Group lies in the disposal of a non-core asset, then we will do so.”