Cornish will oversee the comms, fundraising and direct marketing teams until the end of 2008, whereafter her position will be reviewed.
She has previously worked as a freelancer for a range of charities, including The Children's Society, Trinity Hospice and St Dunstan's.
The Muscular Dystrophy Campaign this week unveiled its report into services for people with muscular disease in Wales. This follows its submission to Parliament in December of a clinician-led report that illustrated vast disparities in service provision for people with neuromuscular disease.
The charity is planning its comms strategy for its 50th anniversary, starting in September. Its key priority in the coming year is to raise awareness of the brand and muscle disease, as well as raising funds for research. It will also launch a network to encourage young disabled people to volunteer and it will teach them how to campaign.
Cornish replaces Drew Cullen, who left last June for the top comms role at the Chartered Institute of Public Finance and Accountancy.
Abby Mardon, who has been acting in the role since, now reverts back to her position as deputy director for marketing and comms.