An autonomous intervention system configured to perform an intervention operation in a wellbore comprises a tool housing having a tool storage compartment configured to house an intervention tool. A valve arrangement permits selective communication of tools and fluid between the tool housing and the wellbore. The intervention system is configured to move in response to an activation event between a tool storage configuration in which the tool housing is isolated from the wellbore by the valve arrangement and an activated configuration in which the valve arrangement is open and the tool housing communicates with the wellbore to permit deployment of the intervention tool by a tool deployment arrangement.