Recently, significant progress has been made in the development of new techniques for the fabrication of mechanically durable, bright, and deformable electroluminescent devices, leading to the emergence of various technologies, such as soft robots, actuators, flexible/stretchable/wearable electronics, and self-healable devices. However, these devices mostly possess coplanar structures, wherein the internally generated light must be transmitted through at least one of the electrodes, and require a thin emissive layer (EML), causing low brightness and less applicability in soft devices. This is particularly challenging in the case of stretchable electroluminescent devices, which require electrodes exhibiting both high transmittance and low resistance even in the stretchable state because thin EMLs have low tolerance to external mechanical deformations. Herein, we report in-plane electric-field-driven, stretchable alternating-current electroluminescent devices with high brightness by utilizing a thick EML comprising multiple parallelly patterned silver nanowires embedded in a zinc-sulfide-embedded polydimethylsiloxane layer. Since the device is driven by an internal in-plane electric field, it can utilize a thick EML without using planar electrodes. At an electric field of 8 V/ μm, the device showed 3.8 times higher electroluminescence luminance than a thin coplanar-structured device and achieved a maximum brightness of 1324 cd/m2 (at 9.12 V/ μm), suggesting that the electric field expands throughout the thick EML. Furthermore, the device exhibited strong mechanoluminescence and good durability of dual-channel luminescence under simultaneous electromechanical stimulation. We believe that our results represent a breakthrough in electroluminescence and mechanoluminescence research and provide important insights into the development of sustainable and stretchable devices with high brightness.