Businessman Sir Tom Hunter has donated the piece, called Night-Time Rituals II, to this year's STV Appeal.
The annual fundraising initiative was launched two years ago by the broadcaster and The Hunter Foundation to help impoverished young people in Scotland.
Sir Tom, an appeal trustee, urged potential buyers to get involved.
"I'm delighted to donate this stunning piece of art in support of the STV Appeal. This is your chance to buy an original work by Jack Vettriano and to change the lives of children blighted by poverty, so dig deep and help the STV Appeal," he said.
Sir Tom acquired the painting last year at a charity fundraising dinner.
The signed oil-on-canvas work depicts a woman relaxing in a bath and is valued at £35,000.
Fife-born artist Vettriano welcomed the donation and urged would-be buyers to bid as generously as they can.
He said: "I was shocked to hear the statistic that 220,000 children in Scotland are living in poverty and I am pleased to have been able to make a contribution to the STV Appeal and to give my ongoing support to this fundraising initiative."
The sale is being handled by Glasgow auction house McTear's via its website gallery1842.com.
Bidding has begun and will end during the live STV Appeal show on Friday October 11. Bidding so far has reached £7,000.
The painting can be viewed in person at Glasgow's Kelvingrove Art Gallery and Museum.