NAC genes, specific to plants, play important roles in plant development as well as in response to biotic and abiotic stresses. Here, a novel gene encoding a NAC domain, named as GhSNAC3, was isolated from upland cotton (Gossypium hirsutum L.). Sequence analyses showed that GhSNAC3 encodes a protein of 346 amino acids with an estimated molecular mass of 38.4 kDa and pI of 8.87. Transient localization assays in onion epidermal cells confirmed GhSNAC3 is a nuclear protein. Transactivation studies using a yeast system revealed that GhSNAC3 functions as a transcription activator. Quantitative real-time polymerase chain reaction analysis indicated that GhSNAC3 was induced by high salinity, drought and abscisic acid treatments. We overexpressed GhSNAC3 in tobacco by using Agrobacterium-mediated transformation. Transgenic lines produced longer primary roots and more fresh weight under salt and drought stresses as compared to wild-type plants. Collectively, our results indicated that overexpression of GhSNAC3 in tobacco can enhance drought and salt tolerances.