The Arabic satellite TV channel al-Jazeera says its editor-in-chief has submitted his resignation.
The station was criticised for its coverage of the Iraq war
According to an al-Jazeera spokesman, Ibrahim Helal said he had had "a tempting offer" from the BBC.
The charity BBC World Service Trust confirmed that Mr Helal was joining to work on a variety of media training projects over the next two years.
Al-Jazeera has been criticised by the US for airing recorded messages from Saddam Hussein and Osama Bin Laden.
Mr Helal said goodbye to colleagues at the channel's headquarters in the Qatari capital, Doha, adding that he had gained rich experience from working at the channel.
He is expected to be replaced by Ghassan Bin-Jiddu, a talk show presenter and the channel's Tehran bureau chief who is regarded as a moderate in Middle Eastern affairs.
Mr Helal first joined al-Jazeera in 1996, when it was launched following the closure of the BBC World Service's Arabic-language TV newsroom.
He has also worked for the BBC Arabic Online service.
Correspondents say that in the Arabic-speaking world, al-Jazeera has for years had a large and loyal audience and a reputation as innovative and hard-hitting.
Its reputation in the West was made during and after the war in Afghanistan, when it broadcast exclusive messages from Osama Bin Laden.
Some officials in Washington have described it as being anti-American and encouraging Islamic militancy, especially since the US-led war in Iraq.