Her departure follows the £6.1bn acquisition of US utility firm Niagara Mohawk holdings, which has doubled the size of National Grid's US interests.
Marcy Reed, head of investor relations since joining last June, has assumed a new role of director of investor and media relations. She will focus on corporate work, with an emphasis on relations with the financial media.
Gareth Lloyd, who was appointed director of communications for the UK business at the time, continues to oversee PR work for the UK arm of the business.
Stevens returns to the US having taken the UK-based lead group communications role following National Grid's acquisition of her then employer, New England Electricity Systems, where she was vice-president communications (PRWeek, 18 February 2000).
Her predecessor, Margaret Stewart, lasted just one year in the post before departing for undisclosed reasons (PRWeek, 12 November 1999).
Stevens was tasked with expanding the firm's corporate communications remit and creating a dedicated group-wide PR function to cover its work in overseas and domestic territories. Previously all PR work had operated out of the group's Coventry base.
National Grid Group was established when the UK electricity industry was privatised in 1990. It now has electricity interests in the US, Argentina, Zambia, Australia and Norway.