The agency won the account after a five-way pitch handled by the AAR.
The brewer's two roster agencies, M&C Saatchi and TBWA\London, pitched alongside WCRS and Farm. The incumbent, Leo Burnett, did not take part.
Conflict with Beck's, which was globally aligned into Lowe in August, forced it to resign the business.
St Luke's will handle the market-leading Strongbow brand as well as the recently launched premium cider, Strongbow Sirrus. S&N's other cider brands, which include Woodpecker, Bulmer's and Scrumpy Jack, will not receive any above-the-line marketing support.
Tim Seagar, the Scottish Courage marketing director, said: "The idea St Luke's presented was differentiating and provocative and translates meticulously across all of our marketing activity."
Neil Henderson, the St Luke's joint managing director, said: "On the eve of our tenth birthday, two Strongbow arrows have thudded into our door. It is the perfect brand for us to celebrate with."