John Lewis put the brief out to pitch following a conflict of interest with Tulchan Communications, which won Debenham's account two months ago (PRWeek, 11 October).
Hogarth will handle a financial PR remit, concentrating on communicating the company's partnership structure.
It is understood the agency won the brief after a seven-way competitive pitch.
John Lewis general editor Paul Burden said: 'We do want to be better understood in the City, because although we're not a public company we do issue bonds, so it's important we communicate with the City press, opinion-formers and analysts.'