Francis joins from her role as director of comms at Prostate Cancer UK, where she has worked for the past seven years, having previously been deputy director of comms and before that head of media and PR.
She has been at the forefront of driving Prostate Cancer UK's new identity and building its mass comms campaigns under the Men United banner.
Francis will oversee all comms, policy and engagement activity at the Alzheimer's Society, including Dementia Friends, the charity's government-supported initiative to change people's perceptions of dementia.
She said: "Dementia is such a key issue facing today's society. You only have to look at the surge of media headlines to see how far the disease is rising up the agenda. I am excited to be joining Alzheimer's Society at such a pivotal point, and looking forward to helping engage people in turning the tide against a disease that affects so many people in the UK, and globally."
Francis succeeds John Grounds, who had held the role in an interim capacity for the past year. He returns to work as a freelance consultant. Grounds also became a non-executive director of charity PR agency Forster Communications in August.
The Alzheimer's Society had an income of £84.4m in 2013/14, and 1,500 staff.