Prideaux joins the insurer in the new role of group communications director. He will take responsibility for Aviva's corporate media relations and internal communications worldwide.
Prideaux was most recently a partner at City PR agency Brunswick, where he worked on Aviva's takeover of RAC in 2005.
He joined Brunswick from a corporate finance role at bank ING Barings in 1995.
Meanwhile, Stimpson, currently group external affairs director, will take up the new role of corporate affairs director for Aviva's UK business, with responsibility for media relations, public affairs and internal communications.