To improve the compatibility of hydrophilic polysaccharide substrates with oregano essential oil (OEO), an OEO Pickering emulsion stabilized by lauric acid-modified cellulose nanocrystals was prepared and incorporated into a cellulose nanofiber/pectin matrix to develop a mango preservation coating. The emulsion prepared at a 0.45:1 absolutely dry mass ratio between lauric acid and cellulose nanocrystals and a cellulose nanocrystal mass fraction of 1.5% showed uniform droplet size distribution and the emulsification index reached 93.7% after 48 h, reflecting good stability. The Pickering emulsion greatly affected the coating’s microstructure, thereby regulating its barrier performance. The composite coating with 1.5% emulsion loading exhibited the best performance with an oxygen transmission rate of 13.25 cm³/(m²·d), a water vapor permeability of 2.59 × 10^-13 g·cm/(cm²·s·Pa), a water contact angle of 76.03°, and 99.69% inhibition against Escherichia coli. In mango preservation trials, the coating reduced the respiratory peak by 14.41%, decreased the mass loss by 3.3% when compared with the control group on day 9 of storage, delayed the browning incidence and the reduction in firmness, and extended the shelf life by over 3 days. In conclusion, the modified cellulose nanocrystals-stabilized Pickering emulsion/nanocellulose/pectin composite coating shows enhanced gas/moisture barrier properties and antimicrobial activity, thereby maintaining postharvest mango quality. It provides an eco-friendly solution for fruit preservation.