The leaders of all the group’s UK agencies – Carat, iProspect, Isobar, Mcgarrybowen, Posterscope and Vizeum – will report to De Groose.
Carat UK will now be led by Matthew Hook, the managing director.
De Groose will continue to report to Rob Horler, the chief executive of Dentsu Aegis Network Northern Europe, who takes on additional responsibilities overseeing the ongoing global development of the iProspect, Carat Enterprise and Data2Decisions brands.
Horler, who also assumes the role of chairman of Dentsu Aegis Network UK, said: "Tracy has been instrumental in creating a strong leadership team, winning new business and driving excellence in performance and capability.
"I have no doubt that Tracy will drive further success for our UK business in her new role and we wish her every success."
De Groose joined Aegis as a consultant in 2009 before becoming Carat UK’s chief executive in September 2010.
She said: "As an executive team, our focus will be on attracting the best talent, driving digital leadership and creating a culture focused on delivering the best business results for our clients."
Dentsu Aegis Network’s mission statement is around "innovating the way brands are built" through best-in-class expertise and capabilities in brand, media and digital communications services.
The network, whose headquarters are located in London, operates in 110 countries worldwide.