He was upgraded to a full squad member in 2014 and played in 10 matches, featuring both at first five-eighth and fullback as Canterbury fell in the tournament's semifinal stage.

As a result of his excellent domestic showings for Canterbury, Mo'unga was named in the Crusaders Wider Training Group for the 2015 Super Rugby season.

However due to the presence of the likes of Dan Carter, Colin Slade and Tom Taylor in the Crusaders backline, he did not get any game time in his first season at Super Rugby level.

[3][8] The 2016 Mitre 10 Cup saw him firmly established in the number 10 jersey for Canterbury, as they went on to be crowned New Zealand champions for the 8th time in 9 years.

This included a Man of the Match performance in the Super Rugby Final played in Christchurch, New Zealand where he scored 17 points to lead the Crusaders to their second consecutive title.

After the Barbarians match, Mo'unga joined the All Blacks for their Northern Tour, having warranted a place in the squad through his performance in the Mitre 10 Cup.

Mo'unga's starting performance against Argentina saw him temporarily overtake Damian McKenzie, as backup to regular starter Beauden Barrett.

[14] He made an appearance in every test on the end of year tour, coming off the bench in the final three, which were wins against England and Italy, as well as a 9-16 loss to Ireland.

With many fans and media alike both favouring the experience of veteran Ben Smith at fullback, and 2 time player of the year, Beauden Barrett, at first five-eighth.

On 28 August 2019, All Blacks Head Coach, Steve Hansen, named Mo'unga as one of 31 players selected in New Zealand's squad for the 2019 Rugby World Cup.

[15] Mo'unga was named as the only specialist first five-eighth in the squad, with the injured Damian McKenzie, as well as single cap All Blacks, Brett Cameron and Josh Ioane missing out.

After a solid display against Ireland in the quarter-finals, Mo'unga and the All Blacks were knocked out of the 2019 Rugby World Cup at the semi-finals against England, losing 19-7.