Warder is one of four directors of JCPR. She has been at the agency for eight years, having previously worked at events company GSP, where she worked on the MTV Awards. She started her career at Freud Communications.
Warder, 33, will assume the JCPR MD role on 1 July, while director Sharon Reid will become deputy MD.
Meanwhile, director Amber O'Connor will join the Edelman Global Client Relationship Management Programme.
JCPR co-founder Jackie Cooper will continue in her cross-agency role of creative director and vice-chair of Edelman UK.
Warder will report to the other agency co-founder, Edelman UK CEO Robert Phillips, and chief operating officer Susan Eastoe.
Phillips said: 'To promote one of our own to such a senior position is always a great source of pride.'
JCPR is now 65-strong and brings in almost £7m in fees, said Phillips.