2011–2014 Murray was selected in Ireland's training squad for the
2011 Rugby World Cup warm-ups in August. He made his Ireland debut against
France as a substitute on 13 August 2011. His second cap came two weeks later against
England, again as a substitute. He was also selected in Ireland's final 30-man squad for the World Cup in New Zealand. Murray's first start, and third cap, came against the
United States in Ireland's opening
Pool C match of the 2011 Rugby World Cup. Murray came off the bench during Ireland's historic 15–6 victory against
Australia at the World Cup. He started for Ireland in their final Pool C game against
Italy, putting a strong performance as Ireland won 36–6. He was retained as scrum-half in Ireland's
quarter-final against
Wales, which Ireland lost 22–10. Murray was selected in Ireland's 24-man squad for the
2012 Six Nations Championship. He made his Six Nations debut when he started for Ireland in their opening match against Wales on 5 February 2012, a game which Ireland lost 23–21. A knee injury sustained in the Test against
France on 4 March 2012 ruled Murray out for the remainder of the 2012 Six Nations, as the injury required a recovery period of 3–4 weeks. Murray retained the Ireland number 9 jersey for the first test against
New Zealand on 9 June 2012. He also started the second test against New Zealand a week later and, during the game, scored his first try for Ireland. Murray started the third test, which Ireland lost 60–0, their heaviest ever defeat. Murray continued in the number 9 jersey for Ireland's opening
2012 Autumn Series test against
South Africa on 10 November 2012. Murray also started in Ireland's uncapped friendly against
Fiji on 17 November 2012, and against
Argentina on 24 November 2012. Murray was named in Ireland's training squad for the
2013 Six Nations Championship on 17 January 2013. He started at scrum-half for Ireland's opening 30–22 win against Wales on 2 February 2013, their 12–6 defeat to England on 10 February 2013, and the 12–8 loss to Scotland. He put in an outstanding performance to win the Man-of-the Match award in Ireland's 13–13 draw with France. He started in Ireland's final game of the tournament, a 22–15 loss to Italy, on 16 March 2013. On 23 October 2013, Murray was named in the Ireland squad for the
2013 Autumn Tests. He started against
Samoa on 9 November 2013. He came off the bench against
Australia on 16 November 2013. Murray regained his starting place for the test against
New Zealand on 24 November 2013, scoring his second try for Ireland during the game, which New Zealand narrowly won 24–22. On 27 January 2014, Murray was named in Ireland's 34-man squad for the opening two fixtures of the
2014 Six Nations Championship. He started against
Scotland on 2 February 2014. Murray started against
Wales on 8 February 2014. Murray started in the 13–10 loss to
England on 22 February 2014. He started against
Italy on 8 March 2014. Murray started the 22–20 win away to
France on 15 March 2014, a win that secured the 2014 Championship for Ireland. Murray was named in the Ireland squad for their
2014 Tour to Argentina on 19 May 2014. He started the first test against
Argentina on 7 June 2014. Murray was named in the Ireland squad for the
2014 Autumn Series on 21 October 2014. He started in the 29–15 win against
South Africa on 8 November 2014, setting up
Tommy Bowe's try. Murray also started in the 26–23 win against
Australia on 22 November 2014.
2015–2018 Murray 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, scoring a try in Ireland's 26–3 win. Murray started against
France on 14 February 2015. He started in the 19–9 win against
England on 1 March 2015. Murray started against
Wales on 14 March 2015. He started against
Scotland on 21 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. Murray was nominated for the
IRUPA Players' Player of the Year 2015 Award in April 2015. Murray was named in the 45-man training squad for the
2015 Rugby World Cup on 24 June 2015. He started the warm-up game against
Wales on 29 August 2015. Murray was selected in the final 31-man squad for the World Cup when it was announced on 1 September 2015. He started in the final warm-up game against
England on 5 September 2015. Murray started the opening pool game against
Canada on 19 September 2015. He came off the bench in the second pool game against
Romania on 27 September 2015. Murray started against
Italy on 4 October 2015. He started against
France on 11 October 2015, scoring the second try in Ireland's 24–9 win. Murray started for Ireland in their 43–20
quarter-final defeat against
Argentina on 18 October 2015. On 20 January 2016, Murray was named in Ireland's 35-man squad for the
2016 Six Nations Championship. On 7 February 2016, Murray started against Wales in Ireland's opening match of the Six Nations, scoring a try in the 16–16 draw. On 13 February 2016, Murray started against France in Ireland's second game of the Six Nations. On 27 February 2016, Murray scored a try in Ireland's 21–10 defeat against England. Murray was nominated for the 2016 6 Nations Player of the Tournament award, alongside Ireland teammate
Johnny Sexton. On 25 May 2016, Murray was named in the 32-man Ireland squad to tour South Africa in a
3-test series. On 11 June 2016, Murray started in the first test against
South Africa, scoring a try in Ireland's historic 26–20 win. On 26 October 2016, Murray was named in Ireland's squad for the
2016 end-of-year rugby union internationals. On 5 November 2016, Murray started in Ireland's test against
New Zealand at
Soldier Field,
Chicago, scoring a try and a penalty in a 40–29 win that was Ireland's first ever against the All Blacks. On 23 January 2017, Murray was named in the Ireland squad for the opening two rounds of the
2017 Six Nations Championship. On 25 February 2017, Murray scored a try and earned the Man-of-the-Match award in Ireland's 19–9 win against
France. Following his performances in the tournament, Murray was nominated for the 2017 RBS 6 Nations Player of the Championship award, alongside teammate
CJ Stander. Murray started in Ireland's wins against
South Africa and
Argentina during the
2017 Autumn Internationals. Murray started every game for Ireland as they won a
Grand Slam in the
2018 Six Nations Championship, scoring tries against
Italy and
Scotland, whilst also earning the
Man-of-the-Match award against Italy and scoring penalties against Wales and England. He started in all three tests in Ireland's historic 2–1
series victory against
Australia in June 2018.
2019–2025 Murray was ever-present for Ireland during the
2019 Six Nations Championship, starting in the 32–20 opening defeat against
England, the 22–13 win against
Scotland, the 26–16 win against
Italy, the 26–14 win against
France and the 25–7 defeat against
Wales in the final round, a victory that saw the Welsh win the grand slam. He was selected in the 31-man Ireland squad for the
2019 Rugby World Cup, having featured in the
warm-up match against
England and the second warm-up against
Wales. During the World Cup itself, O'Mahony started in Ireland's opening 27–3 win against
Scotland, their shock 19–12 defeat against hosts
Japan, the 47–5 win against
Samoa in their final pool game, and in the comprehensive 46–14 defeat against
New Zealand in the quarter-finals, which brought an end to Ireland's 2019 World Cup. Retained by new head coach
Andy Farrell in his squad for the
2020 Six Nations Championship, Murray started in Ireland's 19–12 opening win against Scotland on 1 February 2020, and in their 24–14 win against defending champions Wales on 8 February, and their 24–12 defeat against England, before the tournament was suspended due to the
COVID-19 pandemic. The tournament eventually resumed in October 2020, with Murray starting in Ireland's 50–17 win against Italy and the 35–27 defeat against France in their final fixture of the tournament. With the usual format of end-of-year international tests not possible due to the COVID-19 pandemic, Ireland instead participated in the
Autumn Nations Cup. Murray was used as a replacement in the 32–9 opening win against Wales on 13 November and in the 18–7 defeat against England on 21 November, then started in the 23–10 win against
Georgia on 29 November, and the 31–16 win against Scotland on 5 December, which secured a third-place finish for Ireland in the tournament. Murray was named in
World Rugby's Men's 15s Team of the Decade for 2010–2019 in December 2020. Murray started in Ireland's 21–16 defeat against
Wales in their opening
2021 Six Nations Championship fixture, however, Murray sustained a hamstring during training which ruled him out of Ireland's next three fixtures, though he returned from the injury to start for Ireland in their 32–18 win against
England in the final round. During the
2021 Autumn Nations Series, Murray featured as a replacement in Ireland's 60–5 win against
Japan on 6 November, and in the famous 29–20 win against
New Zealand on 13 November, before replacing the injured
Jamison Gibson-Park to start in the 53–7 win against
Argentina in Ireland's final fixture of the series on 21 November. Murray featured as a replacement in Ireland's 29–7 win against
Wales in their opening fixture of the
2022 Six Nations Championship on 5 February, their 30–24 defeat away to
France on 12 February, their 32–15 away win against
England on 12 March, and the 26–5 home win against
Scotland on 19 March that secured the
Triple Crown for Ireland. He was selected in the squad for the
2022 Ireland rugby union tour of New Zealand, and featured off the bench in the 42–19 defeat against
New Zealand in the first test on 2 July. Murray also featured off the bench in Ireland's historic 23–12 win in the second test on 9 July, in what was Ireland's first ever away win against New Zealand, and in the 32–22 third test win against New Zealand on 16 July that secured Ireland's historic first ever series win in New Zealand. Murray earned his 100th cap for Ireland when he started in their
2022 Autumn Nations Series fixture against
South Africa on 5 November 2022, though he left the field injured during the first half of Ireland's 19–16 win. That injury subsequently ruled Murray out of the remaining Autumn Nations Series matches. After
Jamison Gibson-Park pulled out before kick-off due to injury, Murray was promoted to the starting XV for Ireland's opening fixture of the
2023 Six Nations Championship against
Wales on 4 February, being replaced by Munster teammate
Craig Casey during the second half of Ireland's 34–10 away win. With Gibson-Park also ruled out of the round two fixture at home to
France on 11 February, Murray retained his place in Ireland's starting XV. There was doubt as to whether or not Murray would be available for the match after his father, Gerry, was involved in a road collision with a truck whilst cycling and suffered serious injuries, however, Murray was able to start in Ireland's 32–19 win before being replaced during the second-half. Murray featured as a replacement in Ireland's 34–20 away win against
Italy in round three on 25 February, before returning to the starting XV for the 22–7 away win against
Scotland on 12 March. With Gibson-Park selected to start in Ireland's final fixture of the tournament against
England on 18 March, Murray was used as a replacement in the 29–16 home win that secured the
grand slam for Ireland. During the
2023 Rugby World Cup warm-up matches, Murray featured as a replacement in Ireland's 29–10 win against
England on 19 August before starting in their 17–13 win against
Samoa on 26 August. He was selected in Ireland's 33-man squad for the
2023 Rugby World Cup, and featured as a replacement in their opening 82–8 win against
Romania on 9 September, before starting in the 59–16 win against
Tonga in Ireland's second pool game on 16 September, and featuring off the bench in the 13–8 win against
South Africa on 23 September, the 36–14 win against
Scotland on 7 October, and the 28–24 defeat against
New Zealand in the quarter-finals on 14 October. In February 2025, he announced, alongside teammates
Cian Healy and
Peter O'Mahony that he would be retiring from international rugby following the conclusion of the
2025 Six Nations Championship. ==British & Irish Lions==