Thomas will report to Jonathan Harman, who was appointed chief executive in May, assuming responsibility for the agency's European and global accounts including Vodafone, Mercedes and the recently acquired HSBC.
He will also work closely on clients shared with JWT in a move that reunites him with the agency's European creative head, Craig Davis.They worked together at Saatchi & Saatchi's Asia-Pacific office.
Rmg:black cat was created in February from the merger of rmg:connect and Black Cat. Nelly Andersen, the chief executive of rmg:connect EMEA, said: "Trefor's appointment is part of the evolution of rmg. Trefor will strengthen the creative side with a focus on our recent client win across Europe.
"He is a creative talent who understands the future direction of customer relationship marketing and the consequences of the convergence of broadcasting, computing and mobile telephony."
Thomas has a wealth of experience across direct, digital and relationship marketing. His operation clinched three awards at Cannes - a gold for the NSPCC and two bronzes for St Mungo's. Saatchi & Saatchi X was also a multiple award-winner at ±±¾©Èü³µpk10's Direct Awards this week.
Thomas was made the executive creative director of Saatchi & Saatchi X two years ago after a spell as the regional integrated creative director for Saatchis Asia. He joined from the agency's Singapore office, where he held the post of design director.
Thomas said: "My priority will be to create the best creative work and maximise our relationship with JWT."