The appointment was made last week, but London 2012 head of new media Alex Balfour said it would not preclude the use of other agencies.
This follows a major tender process that included incumbent agency Syzygy, which developed the London 2012 site during the Olympic bid. It said it remains on the project roster.
LBI - the result of the mergers of agencies including Framfab, Wheel, Oyster Partners and LB Icon - has been hired as the lead agency while a smaller, as yet unnamed, shop will be used to enable London 2012 to make quick adjustments to London2012.org.
Balfour explained: "The larger agency will give us the comfort and quality assurance of a big consultancy, while the smaller one will enable us to do things in an agile way and make changes very quickly."
Work will include the integration of a new brand for the London games, due to be unveiled in the next few months.