Biogenic routes for the synthesis of nanoparticles are environmentally friendly, nontoxic, biocompatible, and cost-effective compared to traditional synthesis methods. In this study, cobalt ferrite was synthesized using Zingiber officinale and Elettaria cardamom Seed extracts. Effect of copper contents (x = 0.0, 0.3, 0.6 and 0.9) on the plant extracted Cux(Co1−xFe2O4) was investigated by XRD, SEM, EDX, UV-Vis., PL, FE-SEM, FTIR and photocatalytic activity. XRD results revealed that nanoparticles exhibit a cubical spinel structure with an average diameter of 7–45 nm, calculated by the Debye Scherer formula. The value of the lattice parameter decreased from 8.36 Å to 8.08 Å with substitution of copper, which can be attributed to mismatch of ionic radii of Cu2+ (0.73 Å) and Co2+ (0.74 Å) ions. SEM analysis showed that nanoparticles exhibit a spherical shape (~13 nm diameter) for undoped samples and low Cu concentration, while they changed to a hexagonal structure at higher Cu concentration (x = 0.9) with a diameter ~46 nm and a decreased degree of agglomeration. FE-SEM further confirmed the nanoparticles’ size and shape. EDX analysis confirmed the presence of cobalt, iron, and oxygen without contamination. The optical absorption spectra of UV-vis and PL showed red-shift, which can be accredited to larger crystalline sizes of nanoparticles. FTIR spectra showed two main bands at 410 and 605 cm−1, indicating the presence of intrinsic vibrations of the octahedral and tetrahedral complexes, respectively. The photocatalytic activity of Co0.4Cu0.6 Fe2O4 nanoparticles was investigated using methylene blue (MB) and methyl orange (MO) dyes under visible light irradiation. The degradation rate (93.39% and 83.15%), regression correlation coefficient (0.9868 and 0.9737) and rate constant (0.04286 and 0.03203 rate·min−1) were calculated for MB and MO, respectively. Mechanisms for the formation and photocatalytic activity of Cu-substituted plant-extracted cobalt ferrite were discussed. The Co0.4Cu0.6 Fe2O4 nanoferrite was found to be an efficient photocatalyst, and can be exploited for wastewater treatment applications for MB/MO elimination.