The six-figure brief, which includes public affairs, will see the agency report to Coors head of comms Lesley Allman. G/HI managing director Sue Farr is overseeing the agency's work on the account.
The decision to hand the work to G/HI breaks with Coors' traditional preference for handling corporate work in-house.
The agency now adds the corporate and PA brief to the branding and sponsorship work it already handles for the firm.
In March Coors announced it is to close its Cape Hill brewery in Birmingham after Interbrew retained the brands produced at the site as part of the sale of Bass to Coors.