The online and phone service in England, Scotland and Wales helps people find the projects that most suit them.
It is funded by the Department of Health and NHS England.
Experts say a lack of access to volunteers has hampered critical research into the illness.
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End Quote Sue Boex CarerWe need lots of people signing up in order to find the right people for the right study at the right time”
Dementia affects more than 850,000 people across the UK.
According to government figures, fewer than 5% of people with the condition currently take part in studies.
Researchers are calling for patients, carers and anyone over 18 who is interested in participating - whether they have been affected by dementia or not - to sign up.
By registering with Join Dementia Research, people give permission for scientists to contact them with studies that fit their profiles.
Projects vary from trials of new dementia treatments to surveys looking at how to improve patients' quality of life.
There is no obligation for people to take part and volunteers can opt out if they want to.
The scheme has already been piloted across north London for the last six months, with more than 1,600 people signing up to show interest.
Some 200 have participated in studies so far.
Hilary Evans, of Alzheimer's Research UK, said: "We know there is a strong appetite from the public to play a role in dementia research, but until now there hasn't been an easy and co-ordinated way for people to register their interest."
Sue Boex, one of the carers who helped design the initiative, said: "This is a very exciting initiative and one we really need people to get behind.
"Because studies have very specific criteria, we need lots of people signing up in order to find the right people for the right study at the right time."
Prof Martin Rossor, of the National Institute for Health Research, said: "The government and charities have increased funding for dementia research over the last few years, meaning more studies are being done than ever before, but it is often difficult to find willing volunteers at the right time.
"Growing the number of willing research volunteers will help push forward research to make advances in treatment, prevention and care."
Join Dementia Research is a collaboration between the National Institute for Health Research, Alzheimer's Research UK, Alzheimer's Society, Alzheimer's Scotland and UCL Partners.