Dunaway, who joined Yahoo! in June 2003 from the snack food company Frito-Lay, will leave the internet giant on November 2 after more than four years with the company.
As part of a series of restructuring moves over the past year, nearly half of the 15-member top executive team at Yahoo! have either taken on new roles or left the company. Co-founder Jerry Yang took over as chief executive of Yahoo in June.
In a statement, Yahoo! said: "Cammie has strengthened the marketing function and built a strong bench of creative talent. We wish her all the best in her future endeavours and thank her for her leadership."
In August Yahoo! parted company with its head of global sales, Gregory Coleman and in June, Terry Semel stepped down as chief executive to be replaced by the portal's founder Jerry Yang.
The departures are part of a reorganisation as it struggles to compete with rival Google.
Earlier this month Yahoo! reported a 5% fall in third-quarter pre-tax profits to $151m (£74.2m).