Previously head of UK ad sales, Ballantyne will run the global ad portfolio for Metro's 69 editions in 21 countries.
His predecessor Greg Miall has decided to leave to join a French new-media launch called Sport.
Chris Spalding, vice-president at Metro International, said: "Alistair is the right man to take on this role at Metro International. He has demonstrated his creative sales abilities with us already and is superbly connected, both with agencies and advertisers."
Ballantyne joined Metro in May this year after five years as international group manager at IPC Media on titles such as Marie Claire, In Style and Wallpaper. He was previously at Attic Futura, Leo Burnett and Emap.
He will oversee a team that includes Michael Pennington, who heads overseas sales, and Adam Harris, head of creative services. Ballantyne will begin recruiting a new head of UK sales immediately.
Metro's advertising sales have grown at an annual rate of 44% since the launch of the first edition in 1995, and currently has a daily readership of 18.5m.
The company is currently believed to be bidding for the distribution contract for a new London afternoon free paper.
Five companies have also registered bids, which will allow afternoon distribution in the London Underground and mainline railway stations.
Those believed to be involved include Metro International, News International and Associated Newspapers.
News International is reported to be confident of winning the contract after it registered a name and logo, thelondonpaper, with the Patent Office earlier this year. It is also in talks with Starbucks about further distribution in coffee shops.
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