Ulster have drafted in Terblanche on a three-month contract as emergency cover following an Achilles injury which has sidelined Jared Payne.
Terblanche, 36, has playing experience at fullback, wing and centre.
The utility player, who was capped 37 times by the Springboks, is now awaiting clearance from the UK Border Agency before joining up with his new team-mates at Ravenhill Park.
"At this stage in the season with players all under contract it was always going to be difficult to recruit a high-calibre individual to provide cover for Jared, but we are delighted that we have been able to convince Stefan not to hang up his boots just yet," Ulster's director of rugby David Humphreys said in a club statement.
"Stefan has left us and signed a three-month contract with Ulster," Sharks commercial manager Rudolf Straeuli confirmed.
Terblanche, who became the first player from the union to turn out in 100 Currie Cup matches earlier this season, played his last game for the team in the final of the competition at the weekend.
The defending champions went down 42-16 to the Lions in Johannesburg.
Terblanche was captain of the team when they won the Currie Cup last season.
The veteran back had a previous spell in the United Kingdom when he played for Welsh outfit Ospreys between 2003 and 2007.