Sellars was a member of the first official New Zealand Maori team, in 1910, and became an All Black in 1913, when he toured North America. He was a regular in the Auckland front row during 1909-15, when he joined the New Zealand Expeditionary Force and went to war. He was the first of three Ponsonby
All Blacks to be killed in action — Dave Gallaher and Bill Carson (World War II) being the others. A renowned tough guy, he played in the great 1909 Ponsonby side, one of five men in the pack who had been or would be All Blacks. His consistently strong performances for his club and province caught the eye of the All Blacks selectors in 1913 — no national team having being selected since 1910. A member of the side to North America, he played against Australia at home before leaving. On tour, he was one of the leading players, and one of the busiest, appearing in 14 of the 16 matches. Sellars was killed at Messines, Belgium, while carrying a wounded comrade. He was the first of three All Blacks to lose their lives in that battle within a fortnight. Wing forward Reg Taylor was killed on June 20, while Jim McNeece died of wounds a day later. On the same day as Sellars was killed, another 1913 All Black, James Baird, died of wounds in France.