Thomson joined Global Radio two years ago, following the company's acquisition of Chrysalis, where he had been commercial and operations director.
He played a pivotal role in the acquisition by Global of GCap last year and in the incorporation of the commercial teams into the Global Radio headquarters.
Don Thomson said: "Having been involved for over 24 years in the commercial radio industry, I am delighted to have served a key role in the creation of Global Radio, now the UK’s largest commercial radio group, and to have played a significant part in its success.
"I therefore feel that my job is now done and I look forward to taking on the next challenge and hope Global enjoys continued success."
Stephen Miron, the chief executive of Global Radio said: "Don has made a great contribution to Global Radio and we thank him for all his hard work.
"Whilst we regret his decision, we fully understand his position and wish him every success for the future."
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