Unwin, a former CEO of Cap Gemini Ernst & Young Group, took over from Sir Ronald Hampel in November 2002 and has since then overseen the board as it has continued to narrow its focus to business-to-business media and conferences. He had previously served as a board member for six years before becoming chairman.
The company has made a string of acquisitions and has sold off its non-core business including the sale of market research arm NOP World to German research group GfK for £383m in April 2005 and its 35% stake in UK broadcaster Five to the RTL Group for £247.6m in July of that year.
At the start of this year, UBM bought two firms in China for just over $4.1m (£2.1m) with its acquisition of a medical marketing outfit, MediReach Healthcare Communications, and direct marketing firm, Customer Contact Center Standard.
Unwin will step down as chairman at the end of 2007 and the process to appoint a successor will be led by the board's nomination committee.
Unwin said: "UBM has a clear strategy and a first rate management team who are executing this strategy well. At the end of this year I will have served on the board for 11 years and chaired it for five.
"Therefore I feel it is time, and an appropriate time, to move on. I am making my intentions known well in advance to allow the Board to run an orderly succession process."
Unwin also oversaw the appointment of a new chief executive when Symbian chief executive David Levin took over from Lord Clive Hollick in August 2004.
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