The agency won the business after a competitive pitch against McCann London and DLKW Lowe, which kicked off in September last year.
The NSPCC did not previously retain an agency on the account. In the past, it has worked with agencies including Saatchi & Saatchi and TBWA\London, while Rapp currently works on communications around the NSPCC's ChildLine service.
Inferno will work on both strategic and creative execution for the charity. An initial nationwide campaign will break in the spring encouraging members of the public who are concerned about the safety or welfare of children to contact the NSPCC.
The charity's most recent advertising activity, to support ChildLine, broke in June last year.
Peter Watt, the director of the NSPCC's Adult Advice and Information Services, said: "Inferno impressed us with both its creative vision for the campaign and its clear commitment to supporting the NSPCC's work to protect the UK's most vulnerable children."