J.Walter Thompson rebranded to the shorter JWT in 2005, 18 years after its acquisition by WPP.
The logo being used to promote the 150-year anniversary features an owl and a lamp alongside the agency’s original name.
Bob Jeffrey, worldwide chairman and chief executive of JWT, said: "Throughout our history, JWT has been synonymously referred to as both JWT and J. Walter Thompson. The two monikers peacefully coexisted, in the press, in our own internal communications and by the industry at large.
"In planning for our 150th anniversary, it became abundantly clear that the world and our younger employees in particular, had a deep appreciation and hunger for brand authenticity.
"On 5 December, our official birthday, we will return to the J. Walter Thompson name."