As climate change progresses, mega-fires (large, complex fires burning > 400 km2) are becoming more frequent across many biomes, often in association with intense drought. We analysed five years of stream macroinvertebrate data, collected before and after a mega-fire that burnt >750 km2 of the Grampians National Park, Victoria. The wildfire occurred in 2006, during a 12-year drought (1997-2009). We tested the hypotheses that wildfire alters macroinvertebrate assemblage composition and reduces taxon richness and among-stream variation. Assemblages from five burnt and five unburnt streams were compared before and after the fire, using a multiple before-after, control-impact design. Data from a further 18 streams were used to examine temporal patterns in taxon richness. Streams were sampled in spring each year from 2005 – 2008; a mixture of perennial and seasonally-flowing streams were sampled. Wildfire altered macroinvertebrate assemblage composition and reduced among-stream variation, but was not associated with low reach-scale taxon richness. Fire was associated with increased abundances of predators specialised for soft-sediments and with reduced abundances of shredding and grazing caddisflies. In the short-term, suspension-feeder abundances increased, overwhelming the negative effects of drought on their abundance. Within two years post-fire, assemblage composition in burnt streams was similar to that in unburnt streams. Within three years, among-reach variability in assemblage composition had increased to levels in unaffected streams. Invertebrate assemblages recovered rapidly in these streams despite the large areal-extent of the wildfire. However, the frequency of wildfires is increasing, potentially altering composition and structure of riparian vegetation permanently. As headwater streams depend on riparian vegetation for shading, woody debris and leaf litter, such permanent changes will likely have lasting effects on biodiversity.