Plans to create the Youth Custody Service, which is part of the newly-created HM Prison and Probation Service, were first announced in February by Justice Secretary Liz Truss.
The organisation will be led on an interim basis by Sara Robinson, who takes on the executive director role while remaining director of operations and commissioning at the YJB.
"I am delighted to be given this leadership role and with it, the opportunity to help shape and deliver the reforms to the secure estate, thereby ensuring that the distinct nature of the provision for children and young people, and the voice of the child are fully represented," Robinson said.
"While there are some significant challenges within the sector currently, there is a positive commitment to build upon evidence and implement the changes that will deliver improved outcomes across a range of measures, for the children and young people under our care and oversight.
"The Youth Custody Service will have its own workforce separately recruited and trained to work in the youth estate, and will establish distinct career pathways for those wanting to work with children and young people in the secure estate, including a new youth justice specialist worker role."
Robinson said the role of executive director of the Youth Custody Service will be subject to open competition "in due course".
Numbers of young people held in custody have dropped markedly in recent years - progress that, in part at least, has been attributed to the YJB. As of December 2016, there were 829 under-18s in custody - a drop of 55.5 per cent on the December 2010 figure of 1,862.
However, violence in custody is on the rise and the YJB came in for criticism last year for failing to act on complaints made by young people held at Medway Secure Training Centre, where allegations of abuse were later made.