Eoin Morgan has replaced Alastair Cook as England's World Cup captain, The England and Wales Cricket Board confirmed on Saturday.
Cook has scored just one fifty in his last 22 one-day innings for England and he has paid the price for failing to stop the rot during his country's recent 5-2 series defeat in Sri Lanka.
Morgan will lead the side for the tri-series in Australia after Christmas and then the World Cup in Australia and New Zealand in February and March.
Cook, who turns 30 on Christmas Day, will not be going to the World Cup, the ECB said.
An ECB statement read: "ECB today announced that Eoin Morgan has replaced Alastair Cook as England one-day captain with immediate effect.
"England selectors met yesterday (Friday) to pick a 15-man one-day squad for the tour to Australia and the ICC Cricket World Cup. Selectors recommended to managing director England cricket Paul Downton a change in captaincy which has now been approved by the ECB chairman.
"Cook will continue as England Test captain."