Career
His regular playing position is as a midfield back. Willison played for the Chiefs in Super Rugby from 2009-2012, and was part of the title winning Chiefs in 2012. Also, in 2012 he was selected for the Māori All Blacks end of year tour.
Foreign 2013 Willison was initially included in the Chiefs, before being delisted by coach Dave Rennie while he sought to contract Counties-Manukau midfielder Bundee Aki.
Rennie had intended to sign Aki, then grab Willison back in the draft, but new Blues coach John Kirwan acted quickly to sign Willison and move him to Auckland. At the start of 2014, it was announced that he would leave the Blues after the 2014 Super Rugby season to join French Top 14 side Grenoble on a two-year contract.
On 8 January 2016, Willison joins Aviva Premiership team Worcester Warriors from the 2015-2016 season.