The sealant, paint and varnish brand has shifted its account out of Michaelides & Bednash without a pitch.
The move sees the consolidation of the Ronseal account into MediaCom, which already holds responsibility for implementational planning and buying on the account.
Ronseal is gearing up for a burst of advertising activity in April to raise awareness of its woodcare products as the key outdoor seasons approach.
Alex Debenham-Burton, a MediaCom associate director, said: "We are delighted to add the strategic side of the Ronseal business to the existing responsibilities that we have held for many years.
"The strategic strengths within our agency have made a point of difference in new- business wins over the past few years."
Last December, Ronseal appointed the Principles Agency to manage its creative account and design activity, including brochures and point-of- sale material.
The appointment came after a competitive pitch, following a three-year statutory review. The business was previously held by the now-defunct creative agency Vermillon.
Principles Agency has developed brochures for Ronseal outdoor and indoor living products, in a bid to ensure the brand message is consistent across all its promotional materials. It is currently working on a television and press campaign, which is set to break in Easter and will run until August.
The activity is designed to raise awareness of Ronseal's new Perfect Finish range.
It includes varnish for skirting boards and other hard-to- reach indoor surfaces as well as floor varnish and wood stain for decking.
The advertising will carry the brand's long-running line: "Does exactly what it says on the tin."