In a statement, Byron confirmed it had issued an RFP for a new consumer and trade PR firm.
PRWeek understands that Byron is asking between eight and 10 agencies to send proposals, with a view to shortlist and appoint an agency by August.
The one-year retained contract involves national and local PR support to oversee a regional rollout of around 15 new sites, including Newcastle.
The process is being overseen by brand and marketing executive Claire Strickett.
Amanda Royston, Byron marketing director, said: "As Byron continues to grow into a truly national brand, we’re excited to be on the hunt for an agency that shares the creativity, idiosyncrasy and ambition that have been central to our brand and business from the start."
Byron was founded by Tom Byng in 2007 and recently opened its 52nd restaurant in Canterbury. The chain was sold by the Gondola Group in 2013 for £100m to Hutton Collins Partners.