Unique gut microbial colonisation patterns are associated with the onset of allergic disease in infants; however, there is insufficient evidence to determine if aberrant microbial composition patterns persist in adult allergic rhinitis (AR) sufferers. To compare the gut microbiome composition between adult AR sufferers and controls. Gut microbial composition in stool samples was compared between 57 adult AR sufferers (39.06 ± 13.29 years) and 23 controls (CG; 36.55 ± 10.51 years) via next-generation sequencing of the V3–V4 hypervariable regions of the 16S rRNA gene. Taxonomic classification and identity assignment was performed using a reference-based approach with the NCBI database of 16S rRNA gene sequences. Species richness determined via the Shannon index was significantly reduced in the AR cohort compared to the CG (4.35 ± 0.59 in AR vs. 4.65 ± 0.55 in CG, p = 0.037); trends for reductions in operational taxonomic unit (OTU) counts, inverse Simpson, and CHAO1 diversity indices were also noted. Bacteroidetes (p = 0.014) was significantly more abundant in the AR group than in the CG. In contrast, the Firmicutes phylum was significantly less abundant in the AR group than in the CG (p = 0.006). An increased abundance of Parabacteroides (p = 0.008) and a reduced abundance of Oxalobacter (p = 0.001) and Clostridiales (p = 0.005) were also observed in the AR cohort compared to the CG. Adult AR sufferers have a distinct gut microbiome profile, marked by a reduced microbial diversity and altered abundance of certain microbes compared to controls. The results of this study provide evidence that unique gut microbial patterns occur in AR sufferers in adulthood and warrant further examination in the form of mechanistic studies.