The company has been making its Caledonia Best brand with grains harvested in Scotland since that drink was launched in 2011.
However, for the rest of the portfolio it previously sourced some of the ingredient from outwith this country.
Now it has moved other brands – including Tennent's Lager and Original Export – to Scottish barley with all the products continuing to be made at the Wellpark Brewery in Glasgow.
The change will see Tennent Caledonian buy around 25,000 metric tons of barley from Scottish farmers this year.
John Gilligan, managing director, is pleased the company is able to take the step and hopes it will strengthen relationships with the Scottish farming community.
He said: "At the launch announcement of Caledonia Best we said we were investigating the ability to source [Scottish barley] across the whole portfolio.
"As long-term contracts have unwound we have been able to get to a point where we are now in a place where the standard barley will be 100% sourced in Scotland."
Mr Gilligan is hopeful the move will benefit the company and the farmers involved.
He added: "The comparison for me is grape growing for wine. The growers know they have a route to market and a customer waiting so they can grow accordingly.
"As a brewer you tend to want consistency [of quality].
"Scottish barley is known globally as being among the best in the brewing business, so by working with local maltsters and farmers that we trust, we not only support Scottish suppliers but we ensure our brands are created using the highest quality ingredients available."