[3] Millar first broke into the Otago squad for the 2013 ITM Cup and enjoyed a standout debut season, earning 11 caps and scoring 1 try in the process as the Razorbacks reached the Championship semi-finals before going down to Hawke's Bay.

Injury caused him to miss the entire 2014 New Zealand domestic season before he bounced back the following year playing in all 11 of Otago's games as they once again fell at the Championship semi-final stage, this time losing out 34-14 to Wellington.

[3][6] He made 4 substitute appearances during his first campaign with the Highlanders, not a bad return as he spent the year as the franchise's third choice loosehead behind the more experienced Kane Hames and Chris King.

He did, however, make a comeback with Otago in the second half of 2015 which earned him a recall to the Highlanders wider training group for the 2016 season and this time serving as back up to Daniel Lienert-Brown and Brendon Edmonds, he managed another 4 substitute appearances.

[4] Jamie Joseph announced ahead of the 2018 Super Rugby season that Millar will join his Sunwolves squad alongside several former Highlanders teammates.