Bellamy was commissioning editor for Big Brother from 2001

Bellamy, 35, who has also been head of factual entertainment at Channel 4 since February 2003, replaces Stuart Murphy, who stepped down in October.

BBC director of television Jana Bennett said Bellamy would bring "a new dynamic to BBC Three as it evolves".

BBC Three's success stories since it launched in 2003 include comedies Little Britain and Nighty Night.

Dramas including Casanova and the medical series Bodies have also won critical acclaim.

Hit comedy Nighty Night began on BBC Three

"The BBC is new territory for me and I admire what BBC Three has achieved with new talent and comedy," said Bellamy, who started his career in TV producing and directing documentaries.

"I'm really looking forward to working with Jana to take BBC Three to a new level for audiences."

Weekly high

BBC Three, which is aimed at 25-34 year olds, reported its highest weekly viewing figures in peak time in October, winning 25 per cent of the digital audience.

"I'm delighted Julian will be joining us in BBC Television," said Ms Bennett.

"He has fantastic experience of building channels and brands in a multi-platform digital environment, a very strong creative background and terrific relations with talent and the production community."

E4, whose shows include The OC and award-winning sitcom Peep Show, launched in 2001 as a pay-TV channel aimed at 16 to 34-year-olds.

Earlier this year it became available on the non-subscription Freeview service, in a bid to bolster audiences and increase advertising revenue.