She joins the brand from her role as managing director of Corbin & King, and brings with her experience in running luxury businesses, having begun her career in human resources and operations.
Founder and joint chief Huw Beaugie said: "Zuleika has significant experience not only in operating businesses that deliver exemplary high-end service but also in working closely with founders.
"We very much look forward to working with her and bringing The Thinking Traveller experience to an even wider audience."
The Thinking Traveller founders Huw and Rossella Beaugie will continue to be involved in the business and will work closely with Zuleika during the transition phase.
Fennell said: "I’ve long admired the brand and its laser like focus on delivering unique, unforgettable experiences for travellers by carefully handpicking each of their unique properties."