Having arrived in Otago from South Africa in 2008, Wagner, 32, has played 190 matches for the Volts overall, taking 579 wickets.
But having moved from Mosgiel to Tauranga in recent months he's decided to play locally.
"It's extremely tough to leave Otago; a region that has been extremely good to me and I've been honoured to represent," said Wagner.
"Otago Cricket gave me my first opportunity in New Zealand and for that I'll be eternally grateful. I want to thank all my past and present teammates, the staff at Otago Cricket and the Otago fans for the support they've given me over the past 10 years. Otago will always hold a special place in my heart.
"Having recently moved to Tauranga, logistically it makes sense to represent Northern Districts and I thank them for the exciting new opportunity."
Wagner has played 36 tests for New Zealand and taken 149 wickets.