Among the challenges he faces are maintaining quality and staff morale with less money than his predecessor had for much of his time at the top and negotiating the renewal of the BBC charter in 2016.
He has previously been a current affairs programme-maker and until recently was in charge of the corporation's TV output as head of BBC Vision.
When his appointment was announced in July, BBC Trust chairman Lord Patten said both he and Entwistle thought there was room for improvement and they agreed the BBC could be "10% or 20% better" despite the cuts brought in after the latest licence fee settlement.
Speaking at the time, Entwistle said: "I love the BBC and it's a privilege to be asked to lead it into the next stage of its creative life."
Entwistle joined the BBC as a trainee in 1989 after a short career in magazine journalism. He went on to be editor of Newsnight, head of current affairs with responsibility for programmes such as Panorama and was an acting controller of BBC4.