The broadcaster, which has faced years of decline in its income from traditional advertising, said the video-sharing website's 400 million viewers provided an extended audience which could prove more lucrative than TV advertising.
Although he would not specify terms of the agreement, Bobby Hain, STV's managing director of broadcasting, said the deal with YouTube, which is owned by online search giant Google, would fund new television content in Glasgow.
"On a cost per 1000 viewers basis, the internet (revenue] is very often in excess of television," said Hain.
"This is a really interesting point in time where the internet and television can partner and add value to both platforms.
"You don't have to go very far back when people were calling the TV and internet rivals.
"This is a different era and an age of partnership and collaboration."
STV is the third UK broadcaster to do a deal with Google after Channel 4 and Five.
Last year STV launched its own online TV service, STV Player. Although the broadcaster said the service "continues to grow in popularity" and delivers around 800,000 video streams per month, Hain said only the YouTube deal provided a "worldwide platform".
Matt Brittin, UK managing director for Google, said the YouTube audience which uses and searches for content in a way that TV users cannot, introduced a "new dynamic" to STV viewing.
He added that the deal also brought a younger audience that does not watch as much TV.
"It is a very good way of getting in front of that audience," he said.