Oliver co-founded Fever in 2010, as the consumer PR and social arm of Nelson Bostock Group. Before this she was head of consumer brands at Trimedia (now Grayling) for more than seven years.
Oliver said: "I've had a fantastic time at Nelson Bostock Group and am super proud of Fever and the success we've achieved with the brand since it launched five years ago.
"This seemed like a great time for me personally to choose to step down so that I can spend more time with my son and plan an exciting next step. Thank you to all the wonderful staff and clients I've had the pleasure of working with during this time."
Lee Nugent, CEO, Nelson Bostock Group, added: "We would like to wish Frankie well and express our sincere thanks for the contribution that she has made to Fever and NBG’s success over the years. She was a key player in the leadership team that created and founded Fever and for that we will always be incredibly thankful. We wish her much success in the future."
Oliver's fellow joint MD Bruce McLachlan will continue to lead the agency and there are currently no plans to recruit another joint MD.
Earlier this year Nelson Bostock Group chairman Martin Bostock retired after leading the agency for 28 years.