He was named in the Ireland squad for the opening rounds of the 2015 Six Nations Championship on 1 February 2015. He started against Italy on 7 February 2015. Zebo started against France on 14 February 2015. He started in the 19–9 win against England on 1 March 2015. Zebo started against Wales on 14 March 2015. England's failure to score enough points against France meant Ireland won the 2015 Six Nations Championship, the first time Ireland have won back-to-back championships since 1948–49.