The agency beat three rivals - including incumbent Cavendish Communications - in a fiercely contested pitch. Insight Public Affairs and Mandate Communications (formerly AS Biss) were also involved in the four-way contest (PRWeek, 29 February).
Luther will work across John Lewis's network of department stores, as well as lobbying on behalf of the John Lewis-owned supermarket chain Waitrose.
Last month, John Lewis revealed a sales rise of nearly five per cent for Q2 of its financial year. Under new chairman Charlie Mayfield, the group wants to double in size in the next decade.
John Lewis head of public affairs Charlotte Cool said: 'We chose Luther because of its extensive experience and expertise in using political activity to build up the profile of organisations and shape public policy debate.'
Meanwhile, Mandate will continue to work for John Lewis on a project basis.