Background: The global emergence of antibiotic resistance highlights the urgent need for novel therapeutic strategies, including adjuvants and potentiating compounds, against multidrug-resistant bacteria. Pseudomonas aeruginosa is classified by the World Health Organization (WHO) as a critical priority pathogen due to its high resistance potential and its ability to cause severe nosocomial infections. Beauvericin (BEA), a frequently detected mycotoxin, has been reported to exhibit various bioactive properties, including potential antibacterial and potentiating effects. Methods: The interaction between BEA and a last-resort antibiotic, colistin (COL), was evaluated in seven multidrug-resistant P. aeruginosa isolates using a microplate-based growth assay after preliminary MIC tests. Results: BEA at non-inhibitory concentrations (2.5–10 µg/mL) significantly enhanced the antibacterial activity of COL (1 and 2 µg/mL) in six out of seven isolates, resulting in a marked reduction in residual bacterial growth. Conclusions: BEA exhibited no measurable antibacterial activity at the concentrations used in the combination experiments but acted as a strain-dependent potentiator of colistin activity against multidrug-resistant P. aeruginosa. The observed enhancement of colistin-mediated growth inhibition supports the potential of BEA as an antibiotic adjuvant at clinically relevant colistin concentrations and provides a basis for further mechanistic investigation.