Muncaster, a former sales director at Eurosport and CNN, is leaving Metro to run his own business in Scotland.
Metro has promoted Greg Miall, head of pan-European advertising, to the role of head of international advertising to compensate for the loss of Muncaster.
Muncaster joined Metro International, which has 38 editions in 16 countries, in 2002 from CNN. He is relocating to Scotland to be closer to his family, after commuting from there for the past year.
Miall, 30, joined Metro as international account director two years ago and helped Muncaster to build its international sales team. He became managing director of Metro in Marseille and then commercial director of Metro Poland before returning to London last year.
Muncaster has spearheaded Metro's efforts to increase sales from multi-market deals with advertisers including BA, Dell and Buena Vista. Miall will attempt to build on this activity.
Metro, which targets under-45s in 54 major cities across the world, announced an increase in ad sales of 50% for the first six months of 2004. Its sales of $145m (£80.2m) for this period helped it to produce a second-quarter profit.
Earlier this year, it launched a New York edition and is working with Associated Newspapers, the owners of the UK Metro, to include UK editions in some of its multinational advertising deals.
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