Fellows, a former head of PR for Asda, becomes UK corporate affairs director. She will report to Kellogg's UK MD Greg Peterson.
The company's recent lobbying has included leading the food industry's fight against 'traffic light' labels to help consumers identify unhealthy products. Kellogg's has joined Tesco and PepsiCo to oppose the scheme.
Kellogg's retains Bell Pottinger for public affairs. Fellows said there were no plans to review this business.
Wermann is joining Home Retail Group as director of corporate affairs.