Tipple, who will report to Crumpton, will now take day-to-day control of the agency's planning department.
Chris Macdonald, the chief executive of McCann Erickson, said: "Jon is a top bloke and a great planner. We could have hired someone older, but our plan is to build for the long term, grow energetic and enthusiastic talent, and Jon is hungry for the step up."
Crumpton will now work more closely with senior clients, take a more external-facing role and build the agency's strategic capabilities.
She added: "Jon is a prodigious talent with a desire to be part of our team that is nothing short of infectious. He is ideas-driven but focused on the business, which makes him a great partner in crime."
Macdonald added: "Nikki has achieved everything we planned and more in the two years she's been here.
"It is the perfect time for her to broaden her management role across the agency, with our senior clients, and to help set out our agenda for the future."