Pay, the former Bartle Bogle Hegarty deputy executive creative director, is joining the agency in the newly created role of joint chief creative officer. She will share the title with Maguire, who has been promoted from executive creative director.
The duo, one of the few all-female creative leadership teams, will sit on the agency’s executive management board. They previously worked together at Wieden & Kennedy London.
Pay said: "My next move was all about the team for me – finding the right team with the right ambition. Having known Vicki for over a decade, we’ve always known we would rule one day – it was only a matter of time."
Maguire has been at Grey since 2009 and was promoted to deputy ECD in 2013 and ECD in 2015. Pay, who left BBH last year, has also worked at Mother.
"Vicki and I share enormous self-belief, monster ambition, potty-mouths and the ability to lead generously. We pride ourselves on making our teams and our clients feel anything is possible – and now it really is. This is the best chance in town. Bring it on."
Grey London’s chief executive Leo Rayman praised Pay's "breath-taking ambition" and her ability to galvanise staff.
Of Maguire's promotion, he said: "Vicki has been Grey’s backbone, ringleader and conscience over the past eight years, and in promoting her to CCO, we’re recognizing her unswerving support for our people and our culture and her fierce brilliance in developing and nurturing the world-beating ideas we’re known for.
"Vicki and Caroline are both awarded creatives in their own right and share a passion for a different shape of work. They are peas in a pod, but they also complement each other brilliantly. With these two at the helm we’re unstoppable – together we’re going to take Grey to another level."