The security firm has also undertaken a restructuring strategy, leading to a headcount reduction of 1,100 positions - although only 62 in the UK - and £30 million annualised savings.
Nick Buckles, G4S's CEO, said: "We were deeply disappointed that we had significant issues with the London 2012 Olympics contract and are very grateful to the military and the police for their support in helping us to deliver a safe and secure Games.
"The overall business has performed well in achieving a similar underlying profit as the first half of last year despite economic challenges, particularly in Europe, and weakness in the US government market. Underlying organic growth in the first half has improved to over 5% overall driven by a strong performance in developing markets, which grew by over 10%.
"We continue to see good opportunities from outsourcing around the world particularly from governments looking to improve quality of services and reduce costs and we believe that, with our long-term track record, we will continue to play a major role in this sector.
The breadth of our portfolio in 125 countries continues to present many new growth opportunities. Our market leading businesses, broad customer base and £3.8 billion per annum contract pipeline give us confidence in the outlook for the Group."