Jeremy Newmark, the chief executive of the Jewish Leadership Council since January 2006, is stepping down for health reasons.
Mr Newmark, who is 41, was recently diagnosed with diabetes and related complications which had gone undetected for some time.
He will continue to advise the JLC and assist in a handover as a consultant.
JLC chairman Mick Davis said “Jeremy has made an extraordinarily significant contribution to the success of the JLC and in particular the political advocacy work of our community. I am grateful to him for his enormous dedication to the job and wish him well going forward.”
Mr Newmark, he explained, was “currently not in a position to work at the pace he has been doing over the past few years and which is demanded by this job, given the few resources available at the JLC to the chief executive.”
Mr Newmark, who was formerly a communications director for Chief Rabbi Lord Sacks, presided over an expansion of the JLC both in membership and activity.
His departure means that both the council and the Board of Deputies – who have been discussing unification – are without a permanent professional head.
The Board is currently managed by interim chief of operations Andrea Kelmanson since chief executive Jon Benjamin left in May.