At the 2011 IAAF World Championships in Daegu, Ciaran qualified through a tactical first round - tactical meaning slower than qualifying time of 3:36 pace for early part of the race where strategy of moving faster in latter parts of the race can be used to improve finish order. Ciaran ran 3:36 in the semi-final to qualify for the IAAF World championship final in his first Major Championship appearance. In the final of 2011 World Championships in Athletics – Men's 1500 metres, he placed 10th. Ciaran O'Lionaird of Ireland ran 3:50.12 at 2012 IAAF World Indoor Championships – Men's 1500 metres and placed 22nd. The 2011 World Championship provided him with valuable experience ahead of the London Olympics in 2012. Ciaran did not advance to semi-final at Athletics at the 2012 Summer Olympics – Men's 1500 metres. Ciarán O'Lionáird of Ireland ran 7:50.40 at 2013 European Athletics Indoor Championships – Men's 3000 metres earned a bronze medal. Ciarán Ó Lionáird ran 3:39.79 at 2014 European Athletics Championships – Men's 1500 metres to advance to the final.