Warwicker was a founding member of tomato, the multidisciplinary agency. He brings with him experience in directing both commercials and feature films.
Since launching the agency more than a decade ago, Warwicker has worked in the US, Japan, Sweden and Spain as well as the UK.
He has been involved in a range of projects for a client list that includes Canon, Sony, Coca-Cola, Pepsi, Reebok, Nescafe and MTV.
Alberts arrived at Grey at the beginning of this month from the Sydney-based Mojo Partners agency, as part of the Grey chief executive Garry Lace's recent management shake-up.
Alberts said: "John is one of the most interesting and diverse creatives I have ever worked with. I truly believe he will have a huge impact on the quality and scope of work produced by the agency."
In addition to his commercial offerings for tomato, Warwicker has worked on typography, identity, communication and strategy.
Warwicker added: "While still wanting to remain at the core of tomato, the opportunity of working with Grey was too hard to resist. I have always had a well-travelled scepticism about advertising in general, but the personality and intention of the new team at Grey has, in this instance, changed my mind."