Barnard, who joined Mondelez in March as managing director, Nordics, joined from PepsiCo International, where she held the position of senior vice president and general manager global for the Pepsi-Lipton Partnership.
With a marketing background, Barnard started her career in the UK at Rank Hovis McDougall in 1989, joining PepsiCo in 1997, where she rose to marketing director for Walkers Crisps. In 2003 she was appointed general manager Quaker and Tropicana.
Hubert Weber, president of Mondelez Europe, commented: "Mary’s strong track record and experience of working with power brands make her a perfect fit for this newly created role. Responsible for some of the largest markets in our European business, she will be instrumental in driving growth across our brands including Cadbury, Oreo and belVita."
She replaces Maurizio Brusadelli, who has moved to the Mondelez Singapore business.
Mary Barnard said her appointment came at a "pivotal moment for our business".
"I have enjoyed my first few months in the Nordics and am looking forward to taking on this new role and broader remit," she added.
Last week, Mondelez promoted Dana Anderson to the role of global senior vice president and CMO, as part of an ongoing shake-up of the company's top marketers.
The snacking giant appointed Anderson, who was previously SVP marketing communication and strategy since 2012, to head up the company's global portfolio of advertising, media and marketing.
Anderson's appointment came two months after the departure of Mary Beth West who had previously held the company's top marketing role.
In August, it also announced the appointment of Mark Clouse to the newly-created position of chief growth officer as part of a management shakeup.