The 22-year-old has played for the Auckland Blues Development side as well as Northland in the ITM Cup.
"He is a young prop who can play on both sides of the scrum and I believe he has huge potential," said Connacht coach Pat Lam.
"I know he will continue to thrive and develop in a full-time professional environment."
He added: "I first saw Dominic as he came through the Auckland Schools system and played for the Blues U18s in New Zealand.
"We're looking forward to getting him over for the pre-season as we build towards the start of a new season in both the Pro12 and European Champions Cup."
Robertson-McCoy is Irish qualified through his grandfather, who hails from Mowhan in Co Armagh.
Pro12 champions Connacht have signed  Irish qualified tight-head prop Dominic Robertson-McCoy from New Zealand.