Glen Horton, who turns 26 next month, played 45 games for Otago, and has signed for the Stags on a two-year contract, which is said to be incentive- driven.
Horton first played for Otago in 2002, straight out of Napier Boys High School, and has had an injury-plagued career in the blue and gold jersey. He has had two operations on his shoulders and also suffered hamstring and groin injuries.
His Air New Zealand Cup season with Otago was cut short last year, after he dislocated his shoulder in the match against Taranaki, which required surgery. He is just coming back to full fitness.
Southland chief executive Roger Clark said the side needed a winger and Horton had fitted the bill.
He said with Otago having the likes of Lucky Mulipola, Fetu'u Vainikolo, Karne Hesketh and Ben Smith in the outside backs, the Stags could accommodate the likes of Horton.
He described the signing of Horton as a win-win for Southland, Otago and the Highlanders.
Clark acknowledged Horton's history of injury but felt the fullback had never been well trained and once he got in the Southland environment he could get fitter and become injury-free.
He declined to say the contract was based around playing time but agreed it was incentive-driven.
Fullback options for Otago are not plentiful, although utility back Ben Smith can play there, while former Waikato outside back Armyn Sanders, who has moved south, can play fullback.
