The New Zealander ruptured his Achilles in the recent RaboDirect PRO12 match against Benetton Treviso and faces a lengthy spell on the sidelines recovering.
Stefan Terblanche, who has won 37 caps with South Africa, made his final appearance for the Natal Sharks in last Saturday's Currie Cup final against the Golden Lions in Johannesburg.
The 36-year-old made his debut for the club back in 1999 before joining Welsh region the Ospreys in December 2003.
He returned to South Africa, and the Sharks, for the 2007 Currie Cup season in which he made his 100th appearance for the club.
Confirming Ulster's latest signing, the province's operations director David Humphreys said: "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're delighted that we have been able to convince Stefan not to hang up his boots just yet."
Despite the fact that Terblanche comes to Belfast on a short-term contract, he should settle in quickly with former Sharks team-mates Johann Muller and Ruan Pienaar in the squad.
His arrival date is subject to the time it will take to meet the requirements of the UK Border Agency.