In this work, an analytical method for deltamethrin determination in natural waters based on photochemically-induced fluorescence coupled to third-order/four-way calibration was evaluated and compared with second-order/three-way calibration. The four-way data were obtained during the photodegradation of deltamethrin in the form of excitation-emission fluorescence matrices and modelled by unfolded partial least squares coupled to residual trilinearization (U-PLS-RTL). According to the results, the third-order model resulted in a satisfactory fit and better figures of merit, even in the presence of unexpected interferences due to the additional dimension. In this way, the method presents a limit of detection of 2.9 µg L−1 and a relative error of prediction of 15.8%. The optimization of a dispersive liquid-liquid microextraction (DLLME) procedure reached an enrichment factor (EF) of 5, improving the detection and quantification limits. Finally, the analytical method based on third-order multivariate calibration was applied to quantify this analyte in spiked natural water samples, both directly and after preconcentration. In all cases, the third-order property allowed us to satisfactorily model the data and quantify this compound in these complex matrices, demonstrating the superior analytical performance of the high-order data evaluated.