He takes over from Mark Lund, a former chief executive of Delaney Lund Knox Warren, who has now moved into the same position at the COI. Lund replaced Alan Bishop who is now CEO of Southbank Centre.
McGuinness (pictured) will work alongside AA president Penny Hughes and chief executive Tim Lefroy.
McGuinness started his career at JWT and in 1998 moved to Australia to join M&C Saatchi as a group account director.
In February 2000 he returned to the UK to join TBWALondon, where in June 2001 he was promoted to managing director.
In October 2002, he was then promoted to chief executive, leaving in May 2005 to become a founding partner of BMB.
In March, the AA announced that Lefroy would step in as chief executive to replace Baroness Peta Buscombe
Lefoy moved from his role as chief executive of the change management consultancy Radical Communications to take up the AA position on 5 May.
Buscombe joined the Press Complaints Commission as chairman in April, replacing Sir Christopher Mayer.