Essential oils are natural antimicrobial agents; however, their high volatility and poor stability limit practical applications in food systems. To identify essential oils with strong antimicrobial activity against foodborne pathogens and to improve their stability, the minimum inhibitory concentrations (MICs) of several essential oils against Staphylococcus aureus, Acinetobacter baumannii, and Escherichia coli were determined. Based on the screening results, a mustard-cinnamon-garlic composite essential oil (MCGEO) was formulated and encapsulated using lactose-glycosylated whey protein isolate and chitosan (gWPI-CS) to construct a Pickering emulsion. The results indicated that cinnamon, mustard, and garlic essential oils exhibited low MIC values against all three tested pathogens. The freshly prepared gWPI-CS-EO Pickering emulsion had an average particle size of approximately 348.10 nm and an encapsulation efficiency of 99.85%. The retention rate of MCGEO remained above 83.00% after storage at room temperature for 7 days, indicating good stability. Electron microscopy observations revealed uniformly spherical droplets with a relatively homogenous distribution within the emulsion system. Antimicrobial assays demonstrated that gWPI-CS-EO effectively inhibited the growth of E. coli, S. aureus, and A. baumannii over a 7-day period. Gas chromatography–mass spectrometry analysis identified cinnamaldehyde, diallyl sulfide, and allyl isothiocyanate as the major active components of MCGEO. Overall, the gWPICS-EO Pickering emulsion exhibited enhanced stability and sustained antimicrobial activity. These findings provide a theoretical basis and technical reference for the application of Pickering emulsions to improve the stability, controlled release, and antimicrobial efficacy of essential oils in food preservation systems.