The news comes as it emerges that Richard Elsen has left the agency, which also handles crisis comms and reputation management.
Elsen - who co-founded Bell Yard with Melanie Riley in 2002 - is believed to be working as a freelancer. PRWeek was unable to contact him before press.
Millington's remit is to grow retained corporate and reputation management work, and to advise existing clients.
He has 20 years' PR experience, and was director of Shandwick International's corporate division until 2000, when he joined FD. He left to set up H-PR in 2004.
Bell Yard is working for the ‘NatWest Three', and advised Michael Jackson in 2003 following the Martin Bashir documentary.
Elsen worked for the Labour Party until 1997, when he joined Ludgate Communications.