Armillaria mellea is a major plant pathogen of timber and agronomic crops. Yet, no large-scale “-omics” data are available to enable new studies, and limited experimental models are available to investigate basidiomycete pathogenicity. Herein it is revealed that the A. mellea genome comprises 58.35 Mb, contains 14473 gene models, of average length 1575 bp (4.72 introns/gene). A novel, large-scale proteomic shotgun analysis method, was developed for high-throughput proteomics, applicable to other Armillaria spp. and basidiomycete studies. Tandem mass spectrometry identified 951 mycelial (n = 629 unique) and secreted (n = 183 unique) proteins from A. mellea. Almost 100 mycelial proteins were either species-specific or previously unidentified at the protein level. Signal sequence occurrence was 4-fold greater for secreted (50.2%) compared to mycelial (12%) proteins. Analyses revealed a rich reservoir of carbohydrate degrading enzymes, laccases, lignin peroxidases and large cytochrome P450ome in the A. mellea proteome, reminiscent of both basidiomycete and ascomycete glycodegradative arsenals. Under oxidative stress, A. mellea underwent extensive proteome remodelling within 3 hours and comparative proteomics detected differentially regulated proteins (n = 14). Expression of proteins involved in methionine and polyamine biosynthesis (n = 2) and proteins (n = 2) involved maintenance of cellular homeostasis by regulation of homocysteine levels were significantly upregulated. This response may mitigate against oxidative cellular damage. Proteins (n = 2) putatively involved in the regulation of biosynthesis of specific polyamines were also identified. Remarkably, A. mellea exhibits a specific and significant killing effect against Candida albicans during co-culture. Proteomic investigation of this interaction revealed 205 secreted proteins, with the unique expression of defensive and potentially offensive A. mellea proteins (n = 30). Four proteins expressed in co-cultures were specific to A. mellea, or previously unidentified either by homology or at the protein level. Overall, the data reveal new insights into the origin of basidiomycete virulence, and a new model system for further studies aimed at deciphering fungal pathogenic mechanisms is presented.