Barnes is currently in charge of negotiating format and acquired content rights for programming across Sky One, Sky Two and Sky Three.
When she joins Five in the autumn, she will lead the day-to-day running of its digital channels, including developing their programming strategies. She will report to Hannah Barnes, no relation, Five US and Five Life's director of programmes.
Hannah Barnes said: "I'm delighted that Kate is joining the team. She is an exceptionally talented and creative individual and will be a great asset. Her experience will be invaluable in the ongoing development of Five Life and Five US."
Kate Barnes said: "I am so pleased to be joining Hannah at Five Life and Five US at such an exciting time in the channels' development."
Prior to joining Sky, Barnes spent three years at Flextech, initially as acquisitions and programming executive before being promoted to channel editor of Challenge.