Ewing takes over from current BAA finance director Russell Walls, who is retire later this year. Trinity Mirror said it has begun looking for a successor and would make an announcement in due course.
She leaves Trinity Mirror after a year when it has announced hundreds of job losses and suffered falling circulation, as it suffered due to the volatile advertising market. The company publishes the Mirror, Sunday People, the Racing Post and a host of regional newspapers.
Before joining Trinity Mirror in January 2000, Ewing was partner in charge of UK corporate finance transaction services at Deloitte & Touche.
BAA chief executive Mike Hodgkinson said: "Margaret Ewing has an outstanding record both with Trinity Mirror, where during the past two years she has been instrumental in shaping the merger of Trinity and Mirror Group and has restructured the finance function, and with Deloitte & Touche, where she was a partner for almost 14 years."
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