Group sales and marketing director Shields has been with the retail chain for 27 years, working her up from sales assistant to hold several senior marketing roles including stints as retail marketing director and sales director.
She will be joined on the executive board by group operations director Michael Law. Both will take up their positions on 1 July.
Their promotions have been triggered by the retirement of property director Andrew Varley, who is to leave next year after 22 years with the retailer.
Next has performed well in recent years. It recently announced sales would increase by between 1 and 4 per cent in its current fiscal year, ahead of rivals such as Marks & Spencer.