Carshalton and Wallington MP Tom Brake asked his constituents to pick a charity for him to raise money for over the coming six months.
People were asked to choose between the Riverside Centre, based in Beddington Park, The Liam Charity, which aims to combat teenage suicide, and the Diamond Centre, which gives therapy to disabled people through hose riding.
The results were close, but the Riverside Centre came out on top and will now benefit from Mr Brake's fundraising efforts for the next six months.
A Riverside spokesman said: "We are delighted to have won the vote to be Tom Brake's official charity, particularly over such other worthy causes.
"It's inspiring to know that so many people care about the work that we do and want to actively support our continuing success, and we look forward to working with Tom and his team to build on this in the coming months."
Mr Brake plans to do several fundraising events over the next six months, including the gruelling WildMan trail run.
He added: "As a cat owner myself, I am in awe of the great work the Riverside Animal Centre do with thousands of helpless animals every year.
"I personally know from talking to residents, how much the animal centre is respected and loved for the many animals and families they have helped in Sutton. Now, it’s time for us to help them."
Mr Brake has raised £800 for the charity since announcing his support on June 26.
If you want to help him support the centre, visit justgiving.com/Tom-Brake-MP. If you have any fundraising ideas, email them to firstname.lastname@example.org