Wee Box, Big Change is the annual Lent campaign of the Scottish Catholic International Aid Fund (SCIAF).
Other high profile figures supporting the campaign include actor Robert Carlyle, football manager Ally McCoist and broadcaster Kaye Adams.
The campaign challenges people to give up a treat during Lent and put the money they would have spent on it into their Wee Box for the work of SCIAF instead.
Money raised in the run-up to Easter will go towards the charity's work in parts of Africa, Asia and Latin America.
Last year's campaign raised over Â£830,000, with the money going to communities in the Democratic Republic of Congo, Malawi and Haiti.
Acting legend Robert Carlyle is giving up chocolate to support the SCIAF campaign: "SCIAF is a great Scottish charity that's providing practical help to people in some of the poorest countries in the world – people affected by war, disease, poverty and natural disasters.
"I'm going to play my part in SCIAF's WEE BOX, BIG Change campaign by giving up chocolate for Lent, so they can help more people in need. What will you do?"
It is now the third year in a row that Susan Boyle has publicly supported the campaign.
She said: "It's important that we all have dreams. I'm very fortunate to be living mine. For other people, affected by terrible poverty, war or disease, they dream of peace, good health and having enough food to eat.
"I'm supporting SCIAF's WEE BOX, BIG Change campaign by giving up sweets, chocolate and crisps because I know SCIAF works side by side with people in poor countries to help them overcome poverty and the challenges they face.
"They help people to live their dreams. I'd encourage everyone to join the campaign."
Gold medal winning rower David Smith saw SCIAF's work in Burundi first-hand during a visit last December.
He said: "I've seen for myself the amazing work SCIAF does in extremely difficult conditions in Burundi.
"With money donated by the Scottish public SCIAF is helping so many people become free from hunger and poverty by giving practical help such as agricultural training, seeds and tools.
"When you see the difference SCIAF is making to the lives of extremely poor people every day, you have to help."
SCIAF Director Patricia ChalÃ© said: "We are extremely fortunate to have high profile Scots including Susan Boyle, Robert Carlyle and David Smith, and thousands of Scots across the country taking part in the campaign.
"Their sacrifices during Lent will help SCIAF to support some of the world's poorest people to overcome hunger, poverty, war and disease."