May, who has been at Reed for six years, will join the British Gas parent on 11 September.
She will be responsible for internal and external comms, and has a place on the FTSE-100 company's executive committee reporting to CEO Sam Laidlaw, who joined in July.
‘I was approached by a search company and found the challenge genuinely exciting,' said May. She added: ‘We have to make the stakeholders aware of the changes facing the energy industry. For instance, there is a huge knowledge gap concerning the reasons for price rises.'
May - who replaces Michael Young after he joined Compass Group as corporate policy and comms director in June - said it was ‘too early' to say whether she would be conducting an agency review.
Before Reed, May was a partner at Luther Pendragon.
Reed deputy director of corporate relations Patrick Kerr will assume May's position on an interim basis.