Delegates at the International Fundraising Congress (IFC), held in Holland, voted the children's charity the winner, ahead of The Brooke, Canadian Blood Services, Unicef Mexico and Wateraid, which were all shortlisted.
NSPCC's winning ad for the Childline telephone helpline showed a young girl barricading herself in her room and dialling the Childline number, which rings without being answered.
It was created to show that lack of resources for Childline means the NSPCC is unable to answer one in three calls made to it.
Marcus Missen, development director at NSPCC, said: "Child abuse is a delicate subject but this advert does not over dramatise it.
"It just shows it as it is. The phone rings and rings and the message is that if you can give, this child might get through."
The Gold Star Award is the world's only international competition for charity and NGO fundraising DRTV ads.
Dutch children's charity SOS Kinderdorpen won the Gold Star Award last year.