Mr Fisher, who has also worked for NatWest and currently serves as chief executive officer of ABN Amro, has been an executive director at RBS since March 2006, having previously been chief executive of its manufacturing division.
In his new role, he will oversee IT and operations for the new Lloyds Banking Group - the 'superbank' that will be created by the proposed HBOS merger.
Commenting on the appointment, Lloyds TSB group chief executive Eric Daniels said: "I am delighted Mark is joining us; he has a deep expertise in banking and his proven track record in dealing with highly complex integration activity will be a great asset to the new
Lloyds Banking Group."
Lloyds TSB expects to complete its acquisition of HBOS in January.