British Chambers of Commerce's head of media relations Jo Tanner will leave this week to co-found InHouse with Katie Perrior.
Tanner was a Tory media officer from 1999 to 2002, working under Amanda Platell and Nick Wood.
Perrior has worked for the Tories in two spells: as press officer to former party chairman Theresa May and, more recently, as spokesperson for shadow home secretary David Davis.
Tanner has also worked at the Learning and Skills Council and children's charity the NSPCC. Perrior has previously worked as a freelancer for ITN.