Having won the S. G. Ball Cup with the Roosters in 2014, Manu travelled to Glasgow to represent Australia in an under-19s rugby league nines tournament at the 2014 Commonwealth Games, where Australia finished in second place. Manu moved into the Roosters' NYC team by the end of the year, where he played until 2016. On 2 May 2015, Manu played for the Junior Kiwis against the Junior Kangaroos, playing on the wing and scoring a try in the 22-20 loss at Robina Stadium. On 16 June 2015, Manu re-signed with the Roosters on a 2-year contract. On 14 September 2015, Manu was named on the wing in the 2015 NYC team of the year as he scored 22 tries in 24 matches for the year.
2016
In February 2016, Manu was selected in the Roosters 2016 NRL Auckland Nines squad. In Round 15 of the 2016 NRL season, Manu made his NRL debut for the Sydney Roosters against the New Zealand Warriors, playing on the wing in the 12-10 loss at Mt Smart Stadium. On 5 September 2016, Manu was named on the wing in the 2016 NYC Team of the Year. On 2 October 2016, Manu played on the wing in the Roosters 2016 Holden CupGrand Final against the Penrith Panthers, scoring 2 tries in the comeback 30-28 victory after being down 28-6 at halftime. On 11 October 2016, Manu extended his contract with the Roosters to the end of the 2018 season. Manu finished his debut season in the NRL playing in 3 matches for the Roosters in the 2016 NRL season.
2017
In February 2017, Manu was selected in the Roosters 2017 NRL Auckland Nines winning squad. In Round 7 against the Newcastle Knights, Manu scored his first NRL career try in the Roosters 24-6 win at Hunter Stadium. Manu finished the 2017 NRL season with playing in 16 matches and scoring 5 tries. Manu was overlooked for the Roosters finals series and played for the Wyong Roos in which they made the 2017 NSW Cup against the Penrith Panthers but lost 20-12 at Leichhardt Oval.
2018
On 20 March 2018, Manu extended his contract with the Roosters to the end of the 2020 season. On 30 September 2018, Manu played in the 2018 NRL Grand Final against the Melbourne Storm, playing at centre and scoring a try in the 21-6 win. In the final minutes of the match, Manu was on the receiving end of a kick to the head while he was on the ground by Melbourne five-eighth Cameron Munster in which Munster sin binned for the second time in the match. Manu had an enjoyable 2018 NRL season, playing in 26 matches and scoring 8 tries. The day after the Grand Final win, Manu was selected in the New Zealand national rugby league team 23-man squad for their one-off test against Australia and their tour of England. On 13 October 2018, Manu made his international debut for New Zealand against Australia, playing at centre and scoring a try in a sensational debut as the Kiwis pulled off a 26-24 win at Mt Smart Stadium.
