The agency moved to the SE1 location earlier this year after 10 years in Kingston.
Jason Megson, managing director at GPJ, said: "We have open, working spaces which foster a spirit of collaboration, and then from a creative perspective we have an area for our creative team to work and be inspired and inspire the rest of the agency.
"And community-wise there are many spaces where we can interact both in terms of how we socialise and how we work and conduct our relationships with our clients."