Barns (pictured) joined Nielsen more than 20 years ago and has had leadership roles across all the major parts of Nielsen’s business in that time. Under his leadership, Nielsen has transformed its Watch segment in a rapidly changing media environment with its Total Audience Measurement strategy.

He led a sustained mergers and acquisition strategy that saw Nielsen buy Gracenote and the machine learning start-up vBrand.

James Attwood, the current chairman of the board and managing director at The Carlyle Group, has been named executive chairman and will lead the search for a new CEO.

Attwood said: "Mitch has left an indelible mark on Nielsen – his commitment to integrity, openness, values and engagement will continue to be the heart of this company for years to come."

Nielsen also announced disappointing second quarter results and a strategic review of its Buy segment (which tracks consumer purchases) although it did not give a time-frame for that review.

Revenues were $1.6bn for the second quarter of 2018, up 0.2% (or down 0.7% on a constant currency basis), compared to the second quarter of 2017.

Buy segment revenue for Q2 decreased 4.1% to $789m or 5.4% on a constant currency basis, compared to the second quarter of 2017.

Jamere Jackson, chief financial officer of Nielsen, said: "In the second quarter, we continued to move forward on our multi-year transformations across Watch, Buy, and Operations. However, our progress was not reflected in our financial results, which are disappointing and came in below our expectations, and we are lowering our outlook for 2018."

He added that among the pressures on the business, GDPR and changes in data privacy had impacted its growth rates "as clients and partners grapple with the changes and work to ensure compliance".

The announcement led to up to 27% being wiped off Nielsen’s share value yesterday.