As PRWeek reported yesterday, Unity quit the six-strong agency roster in frustration over the lack of opportunities coming its way and called it "fundamentally flawed".
Red has formally applied to the Government Procurement Service to fill the space left open, highlighting its decade of public sector experience.
Mike Morgan, CEO of Red, said: "We wrote to the Government Procurement Service offering our services based on over a decade of public sector experience… and having people who value and enjoy the challenge of public sector work."
He added: "Public sector work is highly valued by our people because it is professionally rewarding."
The five other agencies on the roster are Engine Group, Munro & Forster, Consolidated, SKV Communications and Syndicate Communications.