Career
Born in Sydney, New South Wales, Koroisau is of Fijian descent and played his junior football for the Berala Bears, before being signed by the South Sydney Rabbitohs. Koroisau played for the South Sydney Rabbitohs New York City team in 2011 and 2012, before moving on to the Rabbitohs New South Wales Cup team, the North Sydney Bears, in 2013. In October 2013, Koroisau was named in the Fijian 2013 World Cup squad.
Koroisau played in 4 matches in the tournament.
2014
In Round 4 of the 2014 NRL season, Koroisau made his NRL debut for the South Sydney Rabbitohs at hooker against the Canberra Raiders in the Rabbitohs 30-18 loss at Australia and New Zealand Banking Group Stadium. On 3 June 2014, Koroisau signed a 2-year contract with the Penrith Panthers starting in 2015.
Koroisau was rated a 7 out of 10 player rating by Rugby League Week for his performance in the Grand Final. Koroisau finished his debut year in the NRL in 2014 season with him playing in 14 matches and scoring a try for the Rabbitohs.
2015
On 24 January 2015, Koroisau was named in the Panthers" 2015 Auckland Nines squad.
On 2 May 2015, he played for Fiji against Papua New Guinea in the 2015 Melanesian Cup. On 2 July 2015, he signed a 3-year contract with the Manly Warringah Sea Eagles starting in 2016, after being released from the final year of his Panthers contract. He finished off his one and only season with the Panthers having playing in 16 matches, scoring 1 try and kicking 4 goals.
2016
In Round 1 of the 2016 NRL season, Koroisau made his club debut for the Sea Eagles against the Canterbury-Bankstown Bulldogs, starting at hooker in the Sea Eagles" 26-8 loss at Brookvale Oval.
