National Grid general counsel and company secretary Helen Mahy has announced that she will leave the company at the beginning of 2013 after 11 years with the FTSE 100 energy giant.

Mahy (pictured), who joined the company through gas trasmissions company Lattice's 2002 merger with National Grid and took over as global general counsel in 2003, is now set to pursue interests outside of the law.

After a six-month handover period, she will be succeeded by Alison Kay, who currently holds the role of commercial director of National Grid's UK transmission business.

Kay, who up until three years ago was UK GC at the company, works with the gas and electricity industries in the UK and Europe to influence the legal and regulatory regimes in which National Grid operates.

Major work Mahy has been involved in during her time in National Grid's legal team has included overseeing the multibillion-pound acquisition of US utility KeySpan in 2007, as well as the company's largest-ever corporate rights issue in 2010.

She also oversaw a 2011 panel review which saw the FTSE 100 company scale back its law firm line-up by 25%, appointing 16 law firms to the roster. Allen & Overy and Linklaters won roles as the company's main corporate advisers, with Berwin Leighton Paisner, CMS Cameron McKenna and Eversheds mandated to advise on commercial, construction and disputes work.

Commenting on her departure, Mahy said: "I have been privileged to work at National Grid, which has had so many interesting challenges for me over the years, as well as having had a wonderful team to support me."

In a Legal Week interview last year, Mahy described how she had set up a company to publish children's stories to raise money for Special Olympics Great Britain. The charity provides year-round sporting opportunities and competitions for adults and children with learning disabilities, whose confidence and health are said to be transformed through sport.