The dashing right-hander has played 21 first-class games - 20 for Canterbury - and has scored 828 runs at an average of 39.42, including two centuries.
Arguably Robertson's greatest achievement came when he scored an undefeated 107 for New Zealand A to help it hold on for a tense draw with the England Lions in March 2009.
He has also played three matches for the New Zealand under-19 team and is a useful right-arm spin bowler, with 17 first-class wickets to his name.
The 27-year-old is in the process of relocating to Dunedin to join his wife, who has secured employment in the city.
He will play for the Kaikorai club and look to press his claims for a spot in the Volts' middle.
That is expected to be a difficult undertaking with Otago well-served, Volts coach Mike Hesson said.
"We had no intention of recruiting batsmen this year," Hesson explained.
"We are pretty confident in our middle order. He'll certainly be involved in our squad but the first month [of the season] is really important for him to prove a point."
Robertson has a wide array of strokes and has been used as a pinch-hitter at the top of the innings.
He got Canterbury off to a flying start against Otago in the 2007-08 State Shield semifinal, dispatching 12 boundaries and compiling a 47-ball half century although Otago went on to win the match thanks to a fine undefeated century from Brendon McCullum.
With Otago employing English professionals Darren Stevens and Chris Nash for the twenty/20 tournament, there is plenty of depth and "to be able to add a player of Iain's quality increases the competition," Hesson said.
But there will be more opportunities to crack the Plunket Shield team and the one-day side.
The international season will likely deprive Otago of the McCullum brothers - Brendon and Nathan - for a good chunk of the summer.
Ian Butler, Aaron Redmond and Neil Broom will also come into contention for spots in the national side.
