The total raised by Sciaf's annual Lent appeal is to be doubled this year under the UK Government's aid match scheme.
The campaign raises money for the charity's work in Africa, Asia and Latin America, tackling hunger, poverty, disease and natural disasters.
The 2018 appeal, to be launched on February 14, will tell the story of families living in one of the poorest provinces of rural Cambodia, who rely on fishing to survive.
International Development Secretary Penny Mordaunt said: "It is vital that we help the poorest people stand on their own two feet. Sciaf's Wee Box appeal is doing just that by protecting the rights of fishermen and farmers in Cambodia and giving them the tools they need to boost their incomes and support their families.
"Every donation made by the generous British public to Sciaf's Wee Box appeal will once again be matched pound for pound by the UK Government, to help some of the most vulnerable people around the world lift themselves out of poverty."
Sciaf director Alistair Dutton said: "This will help us give many more people the help they need so they can work their way out of poverty and have a better future.
"I urge everyone to take advantage of this amazing offer and make sure your money goes twice as far."