In round 1 of the 2009 NRL season, Ah Mau made his first grade debut for the New Zealand Warriors against the Parramatta Eels off the interchange bench in the Warriors 26-18 win. However, after suffering a hamstring injury, Ah Mau did not play first grade again in 2009. His contract was not renewed for the 2010 season, and he signed with the North Queensland Cowboys. Ah Mau finished his debut year in the NRL with him playing in 2 matches for the New Zealand Warriors.
2010
Ah Mau made his first grade debut for the North Queensland Cowboys in round 4, against the Gold Coast Titans playing off the interchange bench in the Cowboys 32-18 win at 1300SMILES Stadium. Ah Mau scored his first NRL career try in the round 22 Queensland derby match against the Brisbane Broncos in the Cowboys 26-34 loss at 1300SMILES Stadium. Ah Mau went on to be named the Cowboys' rookie of the year for the 2010 season, having made 18 first-grade appearances and scoring a try.
2011
On 8 August 2011 Ah Mau signed with the St George Illawarra Dragons on a 2-year deal starting from 2012. Ah Mau finished the Cowboys 2011 NRL season with him playing in 15 matches and scoring a try.
2012
In round 1 of the 2012 NRL season, in the season opener against the Newcastle Knights at Hunter Stadium, Ah Mau made his club debut for the St George Illawarra Dragons off the interchange bench in the Dragons golden point extra time 15-14 win. Ah Mau spent most the year playing for the Illawarra Cutters in the NSW Cup. Ah Mau finished the Dragons 2012 NRL season with him playing in 11 matches.
2013
On 20 April 2013, Ah Mau made his international début, playing for Samoa in the Pacific Rugby League International against pacific rivals Tonga. Ah Mau played off the interchange bench in Samoa's 4-36 loss at Penrith Stadium. In round 24, against the Wests Tigers at the SCG, Ah Mau scored his first club try for the Dragons in the Dragons 16-34 loss. Ah Mau finished the Dragons 2013 NRL season with him playing in 15 matches and scoring a try. On 24 September 2013, Ah Mau extended his contracted with the Dragons for a further two years, until the end of the 2015 season. In October 2013, Ah Mau was selected for Samoa to participate in their 2013 World Cup campaign. Ah Mau played in three of Samoa's four matches.
2014
On 14 February 2014, Ah Mau was selected in the Dragons inaugural 2014 Auckland Nines squad. On 3 May 2014, Ah Mau played for Samoa in the 2014 Pacific Rugby League International against Fiji at Penrith Stadium. Ah Mau played at second-row in Samoa's 32-16 win. Ah Mau finished off the Dragons 2014 NRL season with him playing in 23 matches and scoring a try. On 7 October 2014, Ah Mau was selected in Samoa's 24 man squad for the 2014 Four Nations series.
2015
On 2 May, Ah Mau played for Samoa in their Polynesian Cup clash with Pacific rivals Tonga, playing at second-row in Samoa's 18-16 win at Cbus Super Stadium. On 22 May 2015, Ah Mau re-signed with the Dragons on a 3-year contract, until the end of the 2018 season. He played in every game for the Dragons in the 2015 season, and earned the 2015 Dragons' Player of the Year medal at the Annual Red V Awards Ceremony.
2016
On 7 May 2016, Ah Mau played for Samoa in the 2016 Polynesian Cup against Tonga, where he started at second-row in the 18-6 win at Parramatta Stadium. Later in the year he captained Samoa in their historic test match against Fiji in Apia.
2017
On 6 October 2017, Ah Mau was selected for Samoa to participate in their 2017 World Cup campaign, and played in all four of their matches.
2018
On 9 July 2018, it was announced that Ah Mau had signed with the New Zealand Warriors for three years starting in 2019.
2019
In round 22, Ah Mau played his 200th NRL game for the Warriors in their 42-6 loss against the Sydney Roosters at the Sydney Cricket Ground in Sydney.
