A spokesman said her replacement could be from any sector within the built environment, including landscape or garden design.
"We want someone who has a respected record in the built environment industry, but that could be all sorts of things," he said. "There are lots of challenges to take Design Council Cabe to the next step following the Bishop Review (HW, 21 October) and we need someone who can run all that."
Architect Haigh was director of design review at CABE from 2007 until last April, when CABE merged with the Design Council following Government budget cuts.
She said: "Having achieved the successful merger of the CABE team into the Design Council, it seems a good moment for me to move on to fresh challenges.
"New ways of working are called for to respond to the changing context and a new management team can now take forward the vision."
The watchdog's chief executive David Kester said: "Haigh has been a great asset as an architect, thinker and leader of design review."