Supporting role for an auditor.
Partner Heather O'Driscoll, who is leading the account for HCW, is looking forward to building strong links with the Darlington-based educational charity.
She said: "Charities must keep a very close eye on their finances and are particularly accountable to the public and to the organisations which fund their work.
"Correct handling of finances is a core aspect of NAYT's duties both as a charity and as a limited company."
The NAYT is the flagship organisation for English youth theatre, providing support, training and participation programmes for youngsters aged 11 to 25.
It helps promote youth theatre on local, national and international levels, and is an educational charity and a limited company.
One of its biggest events of the year is the Big Youth Theatre Festival being held in Epping Forest next month, giving groups the chance to share ideas and skills through four days of workshops, performances and celebrations.