Soft actuators based on polymeric materials have immense potential for various niche applications such as soft robotics, shape morphing intelligent structures, smart textiles, sustainable energy harvesting, and biomedical applications. This work demonstrates the use of silk fibroin obtained from the biopolymer Bombyx Mori silk to develop a vapour responsive soft actuator. These silk films are fabricated using a simple facile solution-casting technique, which can be scaled up with relative ease. The unique actuation characteristics of silk films are driven by the water vapour induced stress gradient generated across the thickness of the film, and it possesses sub-second response and actuation times. The excellent durability and consistent performance of the film without any noticeable fatigue are established by subjecting it to more than a thousand continuous actuation cycles. The evolution of secondary structures that usually arise during the fabrication process on the actuation characteristics is studied in detail. Further, the vapour selective shape morphing characteristics of silk films are thoroughly explored. We also demonstrate several potential uses of silk fibroin based soft actuators such as smart switch, intelligent textile layer, autonomous crawler, and caterpillar-like motion.