In her new role Spence will have responsibility for Manning Gottlieb's growing search operation, across search engine optimisation (natural search) and pay per click (paid search).
Spence will report to Katie Eyton, executive director, head of digital at Manning Gottlieb OMD.
Spence was the first dedicated search employee across the Omnicom Media Group when she joined as search manager in 2006.
She was promoted to associate director before becoming search strategy director.
Spence started her career at the Australian full service digital shop The White Agency in 2004.
Previously, Mitchell was head of search across OMD Group. He was promoted to head of search at Omnicom Media Group in April.
Spence said: "I am thrilled about the promotion and the chance to move to Manning Gottlieb OMD.
"The agency’s client list is second to none and Manning Gottlieb OMD is going from strength to strength with significant new business wins and impressive award success already this year.
"In my new role I will be concentrating on ensuring that Manning Gottlieb OMD’s already best-in-class search offering is further strengthened by using the insight we garner through real time trends to influence wider communication strategies."
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