Stirling, a former head of comms for the National Autistic Society, joined the charity in June with a brief to oversee the running of its 12-strong comms team.
But head of comms Janet Wickens confirmed that Stirling left in August with no role to go to.
Wickens would not comment further, but said Stirling had ‘left to pursue other opportunities'.
Before Cats Protection, Stirling - who PRWeek was unable to reach for comment - spent seven years as a consultant, advising on strategic development and implementation for the RNIB, The Disability Rights Commission, The Stroke Association and the Disabilities Trust.