He replaces Sue Percy, who left the RTPI in September to take up the position of chief executive of the Chartered Institution of Highways and Transportation.
RTPI chief executive Trudi Elliott said Parker "would play a critical role in leading the RTPI’s strategy for membership, education, lifelong learning and research."
She added: "Gavin is recognised as a leader in his academic field, nationally and internationally, and brings very strong management experience to the position."
Parker said: "I am delighted to be joining the Royal Town Planning Institute. One of my key priorities will be developing the RTPI’s approach for professional education and accreditation.
"In my new role I also want to help to champion spatial planning, strengthen the knowledge and skills of planners, and to ensure that we set and maintain high ethical and professional standards."
Professor Parker will join the RTPI in April next year on a two year secondment. He will work a four day week in order to allow him to continue to oversee his existing PhD students at the University of Reading.