The Otago Daily Times broke the story earlier in the week, but details of the agreement were unclear.
The club yesterday confirmed the 22-year-old will join the wider training group next year and will then take up a full contract in 2027.
Casey has had a breakthrough season in the NPC, which culminated with a two-try effort in the successful Ranfurly Shield challenge against Canterbury last Saturday.
He was also named the Dunedin division 1 club player of the year for his exploits in helping Kaikorai win the senior banner.
The sight of the young man running around fullbacks and scoring tries like wingers essentially forced the Highlanders’ hand.
He was too good to leave out despite the club having a full roster of loose forwards.
Casey will be hard-pressed to earn a start in the Highlanders’ No 7 jersey, though.
Highlanders Veveni Lasaqa (Bay of Plenty) and Sean Withy (Southland) have shone during the NPC and will not be easily nudged to the bench.
