Both will be responsible for strengthening relationships with customers and media agencies in the UK.
Ellis joins Microsoft Advertising from the National Magazine Company where she was advertising manager for Company magazine. Prior to this, she was client business manager for Hello magazine and Hellomagazine.com.
Mastoras joins Microsoft from Condé Nast, where she was responsible for developing client sales across the company's websites. Prior to Condé Nast, she was digital media manager of the easyJet and Coty account at OMD.
Both report to Damon Westbury, UK head of category management at Microsoft Advertising. He said: "The travel and FMCG sectors both represent huge opportunities for Microsoft Advertising to increase revenue and create more exciting and innovative advertising opportunities."
This article was first published on mediaweek.co.uk