Adecco will be responsible for LOCOG's permanent and temporary recruitment between now and 2012, later supporting staff in the next stage of their careers following the conclusion of the Games.
The employment specialist has previously been a domestic commercial partner for Sydney 2000, Torino 2006 and the Manchester Commonwealth Games in 2002.
"London 2012 will provide us with a unique opportunity to showcase what we do from start to finish, and to demonstrate our expertise in attracting and selecting the substantial workforce who will be delivering these unique world events," said Adecco Group UK and Ireland chief executive officer Catherine King.
"The quality of the people we hire will have a direct impact on the success of London 2012, and having a world-class team will help ensure we deliver a memorable Games," added London 2012 chairman Sebastian Coe.