Rigby, who joined FCB in summer 2003 from sister Interpublic agency Lowe, leaves after discussions with FCB international management about the future strategic direction of the agency.
Banks will oversee the running of the agency along with Scott Hollingsworth, president and CEO for FCB Europe, Latin America and the Middle East, while a new management structure is finalised.
At the same time, Rigby has also reached an agreement with FCB to take the intellectual rights to communications specialist Sandpit, which had been operating under the FCB London banner.
As a result, FCB said Sandpit would be wound down as an offer within FCB London. Sandpit recently picked up the £4m account to launch UltimateBet.com.
According to Rigby, the decision to leave FCB was not an easy one when he has no firm idea where he will land next.
"It wasn't easy making the decision to move without having a firm idea about where next. However, FCB is going in a new direction and that requires a managing director with different passions and interests to mine.
"I'm really sad to leave FCB, but I'm pleased to see the agency brand back on the map in London and wish everyone there all the very best for the future," Rigby said.
Banks himself had been tipped to depart FCB in June, bringing to an end his career in advertising that stretches back more than 40 years.
±±¾©Èü³µpk10 reported that industry sources claimed he will step down as the chairman and chief executive of the agency in June. This is a month before he reaches 60, which is the customary retirement age for senior managers at Interpublic Group operating companies.
Prior to joining FCB, Rigby was head of account management at Lowe. He took over from Sven Olsen, who was promoted to a role at Foote Cone & Belding.
Rigby's own arrival at FCB came on the heels of a management upheaval, which saw the resignation of the management team of managing partners Paul Houlding and Steve Hastings and joint creative directors Dave Alexander and Rob Fletcher, who launched start-up agency Isobel.
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