He began appearing in commercials at the age of 5 and eventually became involved in film and television work while attending St. Patrick's College.
[2] He also landed the starring role in The Duellists, the fifth episode of William Shatner's A Twist in the Tale, with fellow Tribe co-star Victoria Spence.
Initially introduced as the right-hand man of Lex, an early antagonist of the series played by Caleb Ross, his portrayal of Ryan as a trusting and good natured, yet naive socially awkward adolescent, proved a popular character in the series.
Following the series cancellation, Runciman had guest appearances in Dark Knight and, along with another Tribe co-star Jacinta Wawatai, in Revelations during 2002.
After returning from a three-month tour of nine different countries, he started work in a KPMG firm early the next year.