The agency takes over from Edelman, which previously worked on all aspects of Motorola's PR but will now focus on its mobile phone business.
Motorola began operating as two separate companies on 4 January. Motorola Mobility covers consumer mobile, while Motorola Solutions provides comms products for enterprise and government customers.
Chameleon director Steve Lyons said: 'Motorola Solutions' comms challenge is an unusual one. The new brand has to emerge from the shadow of the old Motorola.'