Alzheimer's Research UK has pledged the funds to more than 50 new and existing projects across the country.
The largest grant of £350,000 has been awarded to the Department of Genetics at the University of Cambridge.
Dr Damian Crowther said the money would "provide security" for the department's research into the spread of Alzheimer's through the brain.
Other projects being supported include research into whether existing diabetes drugs could be used to treat Alzheimer's, and the study of biological signs that could aid early detection of the disease before symptoms appear.
The grants represent Alzheimer's Research UK's largest investment into the study of dementia in any one year.
Rebecca Wood, chief executive of the charity, said: "This will go a long way towards helping us find new preventions and treatments for dementia.
"Funding for dementia research lags far behind other serious diseases, meaning new treatments that are so desperately needed still lie out of reach."
She added: "Dementia is not a normal part of ageing, and our scientists hold the key to defeating it, but they need our backing to do it."
The charity estimates that about 820,000 people in the UK are affected by dementia.