He was previously systems director and will replace Tracey Killen, who has been appointed as John Lewis Partnership director of personnel.
Gregory started at the partnership in 1983 and has worked in a variety of roles for both the department store and supermarket chain since then.
John Lewis managing director Andy Street said: 'Eric will bring substantial board-level experience to the leadership of personnel and a proven track record of delivery. This will build on Tracey's powerful legacy and will blend well with the depth of personnel professionalism within the team. It will also set us up very well at a crucial time as John Lewis embarks on its next phase of growth.'
Gregory said: 'Our personnel team is very highly regarded and I'm looking forward to working with them at a time when John Lewis is developing and growing apace.'
Sales at the John Lewis Partnership rose 5.2 per cent to£120.8 million in the week to April 28. However, its department store group reported mixed results, sales were up just 3 per cent to£46.2 million and half its outlets were down compared to last year. Revenue at supermarket Waitrose increased 6.8 per cent to£74.2 million, after a challenging week for the grocer. The retailer said sales were affected by external factors including the London marathon, St George's Day and the earthquake in Kent.