The Alpha Plus Group encompasses 20 independent schools and colleges located nationwide. The schools are favoured by celebrities including Claudia Schiffer for their children.
The most famous schools within the group include Portland Place, Pembridge Hall and Wetherby School, where Princes William and Harry attended primary school.
Chatsworth will provide media relations support, communications training and marketing consultancy services to the group.
Alpha Plus Group chief of staff Anita Francis said: ‘Chatsworth brings a thorough understanding of the needs of the education sector.'