Armitt has been boss of Network Rail since October 2002 and has worked in the rail industry for 14 years. Prior to that he worked on the Channel Tunnel and the construction of the Sizewell B nuclear power plant.
Olympics Minister Tessa Jowell will presumably be hoping that Armitt will last longer than his predecessor Jack Lemley, who resigned in October last year after only 11 months in the chair.
During an ignominious departure Lemley accused Jowell of being unrealistic about the true cost of London's 2012 Games.
Speaking of Lemley's successor, Jowell said: 'I am confident that under John's leadership, the ODA will ensure that London 2012 will be remembered not only for fantastic sport, but also inspiring venues, a legacy of world-class sporting facilities, and the regeneration of one of the most deprived areas of the UK.'
Acting chair Roy McNulty will resume his role as deputy chair when Armitt takes up his position on 1 September.
A spokesman for the ODA said it was too early to expect Armitt to comment on fears that the design of the London Games would suffer owing to the ODA's preference for Design and Build-led procurement.