The agency has been brought on board as the brand steps up its marketing efforts in a bid to retain existing customers and win further market share.
The agency was awarded the account without a competitive pitch.
Threepipe is charged with handling the PR for new menu launches and restaurant openings as part of its brief. The agency will also aim to support the restaurant company's loyalty programme GBK Brand, which was launched earlier this year.
Threepipe co-founder Jim Hawker will lead the account, reporting to David Sykes at Clapham House Group, which owns the GBK brand.
‘We will be working closely with GBK to communicate all that innovation and to distinguish GBK from the wide high street choice,' said Hawker. ‘We will be helping GBK communicate the strength of the brand at a time when many restaurants are closing.'
GBK has recently launched its 50th restaurant on Clink Street in London, which Threepipe will be helping to promote.
GBK is set to launch a new style of restaurant featuring smaller-sized burgers in an effort to encourage greater frequency of visits from customers.