The Central England Co-operative has raised more than £1.1m for Dementia UK over the past two years and will extend the partnership for another 12 months.
More than half of the money raised came from donations and £500,000 has been raised by the 5p carrier bag levy.
Central England Co-operative, which offers food, travel and funeral services, employs more than 8,000 staff in more than 400 trading outlets across central England.
Fundraising events carried out by the company’s staff included skydives, sponsored swims, cake sales and community events.
Dementia UK supports families through its Admiral Nurse service, which provides one-to-one support and practical advice to people with dementia and their families.
The partnership has funded training and development for the charity’s Admiral Nurses, its Admiral Nurse Dementia Helpline and Admiral Nurse clinics.
Debbie Robinson, chief executive of Central England Co-operative, said: "To have raised more than £1.1m in the two years of the relationship is a wonderful achievement, and to know it has helped to improve the lives of those living with dementia and their families is truly humbling."
Hilda Hayo, chief executive of Dementia UK, said: "We’d like to say a huge thank you to Central England Co-operative in supporting us so we can be there for every family who needs specialist dementia support."