Interferons (IFN) provide a critical first line of defence against viral infection in vertebrates. Moreover, the IFNλs, a recently identified group of mammalian IFN, has demonstrated antiviral potential in the treatment of viruses. With the growing concern over diseases, such as avian influenza, there is a pressing need for new antiviral strategies and the use of immune molecules, such as IFNλ, provides an attractive option for treating poultry by augmenting the host response to virus. With this in mind, we cloned and expressed the chicken orthologue of IFNλ (ChIFNλ) and assessed the biological activity and anti-viral potential of this avian cytokine. Analysis of the expressed recombinant ChIFNλ showed that, similar to the observations with mammalian IFNλ, ChIFNλ has viral inhibitory properties similar to that observed for type 1 IFN. Additionally, although ChIFNλ did show activity similar to type 1 IFN, ChIFNλ could be distinguished from type 1 IFN as it had dissimilar induction properties and was associated with the induction of different genes. Furthermore, we have also used ChIFNλ in in ovo and in vivo trials and have shown that ChIFNλ also has the capacity to augment vaccine responses. We were able to demonstrate that ChIFNλ was able to increase responses to CAV ~5 fold and 10 fold for the primary and secondary immunization, respectively. The observed antiviral activity demonstrated by ChIFNλ supports its potential inclusion in therapeutic strategies directed against viral infections.