Harsh freezing and high-humidity environments lay down paramount bottlenecks for the utilization prospect of polymeric electromagnetic interference (EMI) shielding materials. Herein, ultrathin and flexible multifunctional EMI shielding MXene/Ag nanowires/poly(3, 4-ethylene dioxythiophene):polystyrene sulfonate (MXene/AgNWs/PEDOT:PSS) composite coatings were fabricated via the facile drop-casting of MXene/AgNWs/PEDOT:PSS mixture dispersion and subsequent hydrophobic spraying modification. Profited by the superior electrical conductivity of both polymer host and filler guests, MXene/AgNWs/PEDOT:PSS coatings exhibit the preeminent EMI shielding effectiveness (SE) of 31.5 dB at a rather small thickness of 10 µm, far surpassing that of most the reported polymer-based EMI shielding composites at the similar thickness. Moreover, MXene/AgNWs/PEDOT:PSS coatings also hold excellent electro/photo-thermal transition ability and fascinating water repellency, which ensures their normal application on cold and damp conditions. Interestingly, the intensive interlocking effect of 1 D AgNWs and 2 D MXene allows the wonderful interfacial adhesion and mechanical durability of MXene/AgNWs/PEDOT:PSS coatings. This study provides a valuable insight into the design and construction of multifunctional polymeric coatings for EMI shielding of high-power and high-frequency electronics in cold and high-humidity environments.