He has been hired to head its newly created media investment unit, which will aim to help clients maximise their adspends by calculating levels of return on the money they deploy against different media and buying patterns.
Jacobs will be based in London but will report to Millward Brown's US-based global chief executive, Bob Meyers.
Jacobs joined Aegis in the early 90s to work with its then chief executive, Crispin Davies, on growing its operations outside Europe. He was later appointed as the managing director of Carat International but left to join Universal following differences with Aegis over Carat's future direction.
His book Spending Advertising Money, co-authored with the late Dr Simon Broadbent, is considered a major work on UK media research, planning and buying.
Jacobs said: "My role will be to look at how we can measure media effect and to marry the data from all sources so that clients are better able to manage their budgets."