A former Sawtell resident, Greenshields attended Toormina High School, who compete every year in the Robbie MacKinnon Cup against other local schools of the Coffs Harbour district. His junior club was the Sawtell Panthers JRLFC, a club recently crowned Group 2 senior champions.
He moved to the Catalans Dragons in 2007 and took the role as first-choice full back, becoming a key player. On 10 May 2008 it was announced that Greenshields has signed a new three-year contract with the French Super League club.[5]
Greenshields was named in the 2008 Super League Dream Team, beating world class talents like Brent Webb and Paul Wellens to be named as the outstanding full back of the Super League season. He was also one of the front runners for the Man of Steel award in 2008.[6]
Greenshields signed a one-year extension to his deal at Catalans Dragons in July 2011.[7]
Greenshields returned to the NRL in 2013, signing with the North Queensland Cowboys, for whom he played 6 times, scoring three tries. He subsequently declared that the 2013 NRL season would be his last as a professional rugby league player, and announced his retirement at the end of the year.[8] However, he later changed his mind and went on to win two Group 2 grand finals, 2017 and 2019 with the Grafton Ghosts.