This year, Shelter Cymru has estimated that more than 1,500 children in Wales face Christmas without a home.
In the past 12 months, the number of people turning to the charity for advice and support has increased by more than a third.
The donation follows a commitment from Monmouthshire to support Shelter Cymru as its charity partner until 2026.
This Christmas the charity has emphasised the number of children living in hostels, B&Bs, hotels or flats with insufficient space for eating sleeping and playing.
It has also launched its Super Santa appeal, asking for the gift of high street vouchers that can be given to those facing homelessness this Christmas.
Kerys Sheppard, head of fundraising at Shelter Cymru, said: “Right now, there are thousands of people in Wales facing a winter on the streets or in temporary accommodation.
“Thanks to the generosity of the Monmouthshire Building Society we are able to support even more families who are facing the devastating impact of the housing emergency.
“The donation of £1,000 to our Super Santa appeal and £4,000 to our front line services will make a big difference to many people.”
Dawn Gunter, chief operating officer at Monmouthshire Building Society, said: “Shelter Cymru are about to face a third year of pressure as the impact of COVID-19 continues.
“With increased demand for the advice and support they provide we felt it was right to make a donation that would provide a boost to frontline services and help make this a happier Christmas for some by contributing to the Super Santa appeal.
“At the Society we believe that everyone has the right to safe and secure housing and we are looking forward to developing our relationship with Shelter Cymru over the next 5 years.”
Penny Salter from Shelter Cymru added: “A voucher might not seem like a huge gesture but for some, this could be the only gift they receive this year.
“This small act can have a truly positive impact on someone and make their Christmas that little bit happier.”
