The latter has been labelled as 'the mouthpiece of Osama bin Laden' by critics such as the Bush administration.
The company has been on the hunt for an international agency since the beginning of the year (PRWeek, 21 January). BLJ will promote the new channel, which launches next year, as an independent news source. Bell Pottinger and three unnamed US agencies also pitched for the work.
Based in Qatar, Al Jazeera International will be the first English-language news channel based in the Middle East.
It aims to 'provide the news that matters to the English-speaking world as seen through the eyes of the free press of the Arab and Muslim world'.
BLJ executive vice-president Mike Holtzman will lead the 'significant budget' account, handled by five staff in London and nine others across Washington DC and New York.
A brand-building drive will target the US media to 'soften entry to global markets'. The second and more ambitious phase will see BLJ promote the channel's 'complete editorial independence' from its sister Arabic channel.
The channel's presenters will include ex-BBC and CNN anchor Riz Khan.
BLJ's other media clients include the Telegraph Group and the BBC in the US.