[3][4] Waerea-Hargreaves was signed by the Manly-Warringah Sea Eagles recruitment manager, Noel Cleal, despite never having played rugby league.

Waerea-Hargreaves made his NRL debut against the Brisbane Broncos in round 9, playing off the interchange bench in the Sea Eagles 22–20 win at Suncorp Stadium.

[6] In his next match, in round 15, Waerea-Hargreaves scored his first NRL career try in the Sea Eagles 20–14 victory over the Canberra Raiders at Brookvale Oval.

[11] In week 1 of the finals, against Wests Tigers, Waerea-Hargreaves was on a receiving end of big hit from Simon Dwyer.

[12] Waerea-Hargreaves played off the interchange bench in the 2010 NRL Grand Final, losing 32–8 to the St George-Illawarra Dragons.

[23][24] In round 11, against the Canterbury-Bankstown Bulldogs at ANZ Stadium, Waerea-Hargreaves played his 100th NRL career match in the Roosters 32–12 win.

In December, the Canberra Raiders offered Waerea-Hargreaves a multimillion-dollar contract but ended negotiations after he failed to meet a deadline.

In round 9, against the Newcastle Knights, Waerea-Hargreaves made his return for the Roosters from injury, playing off the interchange bench in the 38–0 win at the Sydney Football Stadium.

On 30 September, Waerea-Hargreaves played in Eastern Suburbs 21–6 victory over Melbourne in the 2018 NRL grand final winning his second premiership as a player and the roosters 14th.

[46] Waerea-Hargreaves played a total of 23 games for the Sydney Roosters in the 2021 NRL season including the club's two finals matches.

[47][48] In round 24 of the 2022 NRL season, Waerea-Hargreaves was sent to the sin bin for a dangerous high tackle during the Sydney Roosters upset victory over Melbourne.

[49] In the elimination final, Waerea-Hargreaves was sent to the sin bin for a dangerous tackle in the club's upset defeat to arch-rivals South Sydney which ended their season.

[50] In the third group stage match at the 2021 Rugby League World Cup, Waerea-Hargreaves was sent to the sin bin for a stiff arm to the head of Dan Norman during New Zealand's 48-10 victory over the Republic of Ireland.

In round 26 of the 2023 NRL season, Waerea-Hargreaves was placed on report for a high tackle on Wests Tigers player Apisai Koroisau.

[54][55] In round 10 of the 2024 NRL season, Waerea-Hargreaves played his 300th game for the Sydney Roosters in their 38-18 victory over the New Zealand Warriors.