Sadler left Ford last October after five years at the motor company, where she was director of government affairs for Ford of Britain. She oversaw its relationships with government, regional assemblies, Whitehall and local authorities. She also liaised with its UK and US boards on national and EU directives.
It is believed that she will advise Miliband – seen as a potential future prime minister – on some policy aspects of his brief at the ODPM, as well as being his top comms aide. Sadler will work alongside his existing special adviser on policy Tim Williams.
Miliband, who has a reputation as a Blairite intellectual, entered the Cabinet following last May's general election. He has gone on the record to back Gordon Brown as the next Labour leader, but has been tipped as a likely challenger should the Chancellor's standing relative to Conservative leader David Cameron deteriorate. His brother Ed Miliband is one of Brown's closest aides inside Westminster.
On Tuesday this week, Miliband set out a vision for devolving power from the state and local authorities to individuals and community groups. He dubbed it 'double devolution', citing neighbourhood police teams and tenant management bodies as examples.
A local government white paper this summer is expected to detail how this will be implemented.
On Sadler's hire, an ODPM spokesman said: 'We're not in the position to say anything at the moment.'
Sadler's responsibilities at Ford have been assumed by Andrew McCall, who previously managed government relations for the company's Jaguar, Aston Martin and Land Rover marques.