Perrior co-founded iNHouse with Jo Tanner in 2006 and left when she took the role at Downing Street following May’s appointment as Prime Minister last summer.
Tanner said: "This has been a fantastic year for the company. After significant growth in recent months, we have decided to invest heavily to bolster our senior counsel and ensure we can continue to provide our clients with the best advice and support.
"I am thrilled Katie is coming back to the company as chair, enhancing the fantastic offer we now provide. Our unique style continues to stand out in the market with a unique blend of creative campaigns, crisis comms, public affairs, in addition to our successful innovations like the Party Conference London Lounge."
Perrior said: "Over the past year I have occupied a top seat at the heart of Government, leading the communications strategy domestically and abroad, as well as understanding how Government really works. I hope to bring my knowledge to iNHouse as its first chair, supporting the company I helped establish as it enters this exciting time."
The news follows the appointment of Michelle Di Leo, who led the public affairs team at FleishmanHillard Fishburn, as a partner at iNHouse.
Perrior, a long-time Conservative party member and activist, was critical of the party’s campaign in the run up to the General Election in an article in The Times, particularly regarding its election policy on social care.
She renewed her criticism following the General Election last Thursday, saying May was "badly advised" during the campaign.
INHouse said Perrior's appointment has been approved by the Advisory Committee on Business Appointments, which considers business appointments for former ministers, senior civil servants and other Crown servants.