The 'Bleeding Love' hitmaker has been a patron and trustee of the Essex sanctuary - which provides a safe and loving home for abused, abandoned and neglected animals - for several years, and now she is set to be joined by her former 'X Factor' mentor Simon, the American songwriter, 'Say You Won't Let Go' hitmaker and the EDM DJ-and-producer in her work.
Leona said: ''I am so thankful to my kind friends for joining me in my mission at Hopefield Animal Sanctuary to promote humane behavior towards animals all over the world, starting right at home for me in the UK.
''Their support of the sanctuary will help us to continue to rescue those animals most in need who have been abused, abandoned or neglected. I look forward to working closely with our ambassadors in raising awareness and funds.''
Music mogul Simon has called on animal lovers to get involved with the charity's work.
He said: ''As a huge animal lover when Leona told me about the work that they are doing at Hopefield Animal Sanctuary I immediately jumped at the chance to help support. The passion that I felt from Leona was immense and the way she described some of the individual rescue stories to me has made a huge impact.
''They provide a safe home for over 500 animals on 53 acres in Essex and are positively changing the lives of animals that would otherwise have very different stories.
''I am excited to be an ambassador for them and help bring awareness to their work.
''Leona can't do this alone and will need help from others who also love animals.
''Any support will be much appreciated and will make a difference.''
Steve said: ''I'm lucky enough to have the opportunity to travel the world with my music, which has allowed me to meet and interact with people and animals from all over.
''This global focus is something Hopefield Animal Sanctuary in England embodies as well by caring for so many mistreated, neglected and sick animals from all around the world.
''They actively work to raise awareness for better animal welfare worldwide, and that is something that resonates deeply with me. I'm honoured to be an ambassador for such an amazing cause.''
Pop star James is delighted that Leona enlightened him to the ''amazing'' work Hopefield do and can't wait to spread the word with his fans.
He commented: ''The work that Hopefield Animal Sanctuary does is simply amazing - the way they impact animal lives in such a transformative and positive way, giving abused, mistreated and sick animals a forever home makes me feel so proud to be involved. I needed to be a part of the work that they do.
''I'm so happy Leona brought this special place to my attention and I can't wait to let my fans worldwide get to know more about them.''
Diane previously teamed up with Leona on the 2016 charity single '(We All Are) Looking for Home', which was released in support of ending the suffering and torture of dogs around the world, in particular the Lychee and Dog Meat Festival in China.
The 'Because You Loved Me' songwriter added: ''I am very proud to be an ambassador for Hopefield Animal Sanctuary in the UK.
''They have been rescuing unwanted and mistreated animals in need for over 30 years, giving them a safe loving home and the medical attention they need.
''Leona has been telling me about them and their mission for years.
''As a sanctuary they do rely on public support so I wanted to lend my voice to help raise awareness of this magical place and the great work they are trying to do.''
Leona has designed festive jumpers, with 100 per cent of the proceeds being donated to Hopefield.
To donate and find out more head to hopefield.org.uk/donate