This study aimed to investigate the antibacterial and antibiofilm activities of the essential oils of Cuminum cyminum (CEO) and Foeniculum vulgare (FEO) on the clinically isolated Porphyromonas gingivalis (P. gingivalis) and Prevotella intermedia (P. intermedia). Subgingival plaque samples were collected from periodontal pockets (≥6 mm) of patients with generalized severe periodontitis. Microbiological and molecular tests were performed to isolate and confirm P. intermedia. A previously isolated P. gingivalis was used. The hydrodistillation method was used to extract the CEO and FEO. The antibacterial activity of the examined oils against the confirmed clinical strains was determined using the disc diffusion and broth dilution methods to determine the minimum inhibitory (MIC) and bactericidal concentrations (MBC). The antibiofilm properties of CEO and FEO were determined using the tube method. The t-test was used for comparisons of inhibition zones. Both CEO and FEO presented inhibition zones against both clinically isolated bacteria. The CEO and FEO revealed antibacterial activity with MIC values of 3.125 µL/mL and MBC of 6.25 µL/mL against P. gingivalis, respectively. In addition, their MIC and MBC against P. intermedia were 0.195 µL/mL and 3.125 µL/mL, respectively. Finally, the essential oils showed moderate to strong antibiofilm activities against the clinically isolated P. gingivalis and P. intermedia, respectively. This study supports the antibacterial and antibiofilm properties of CEO and FEO against clinically isolated P. gingivalis and P. intermedia. Further studies should focus on using these essential oils as an adjunct to periodontal therapy.