Tee has joined the board after leaving the Government in March, having recommended the closure of the COI in his review of government comms.
Tee is not being paid for his advisory role. It is not known if he has taken any paid roles yet.
A Cabinet Office list of meetings held by permanent secretaries reveals that Tee met with Blue Rubicon last November to discuss 'government comms'.
A spokeswoman for Blue Rubicon said: 'Matt Tee has joined Blue Rubicon's advisory board, adding his considerable expertise to other members.'
Existing members include Krow founder Barry Cook and Luther Pendragon founder Charles Stewart-Smith.
Tee was not available for comment at the time of going to press.