Tahu started his career in the National Rugby League for the Newcastle Knights, with whom he won the 2001 NRL Premiership before moving to the Parramatta Eels.

Tahu played in the Knights 2001 premiership side, scoring a try that cemented the victory as Newcastle defeated Parramatta 30–24.

In Tahu's final game in the NRL, he was put on report for a head slam on Melbourne Storm player Israel Folau.

Tahu made his debut performance in the Super 14 competition in the Waratahs clash with the Wellington Hurricanes on 16 February 2008.

[citation needed] During the 2008 Pacific Nations Cup, Tahu repeatedly performed for Australia A, playing at both wing and inside centre.

On 6 July Tahu played a pivotal role in the Australian A's final Pacific Nations Cup game against New Zealand Maori, scoring 2 tries.

[17] On 22 July 2009, it was announced that Tahu would return to league and would rejoin his former club, Parramatta Eels on a three-year contract in 2010.

[18] In 2010, Tahu earned a recall to the New South Wales State of Origin team and was involved in a race-related incident with assistant coach Andrew Johns.

In New South Wales Blues training, Johns reportedly called Greg Inglis "a black cunt".

Johns was reported as telling centre Beau Scott he needed to stop Greg Inglis, and made a racial reference to the Maroons Aboriginal star.

[23] After the tumultuous 2010 season, Tahu requested an extended break from the Eels pre-season training, hoping to return in January 2011.

[30] On 24 April 2016, he came off the bench and played a role in Denver's game in San Francisco only a few days after he had moved to the United States from Australia.