De Beer toast of Saracens.
De Beer, 29, has recovered from a knee injury that has kept him out of action since May last year and will act as cover for fly-half Duncan McRae at the London club.
'Jannie is a wonderful player and a fantastic goalkicker,' said Saracens chief executive Francois Pienaar, who guided South Africa to their World Cup triumph on home soil in 1995.
'Given that Thomas Castaignede is out of action through injury, and the problems that arose when Tim Horan and Duncan McRae were injured at the same time, we wanted to ensure that we go into the play-offs in the strongest position possible.
'Jannie was approached by various Super 12 sides, but expressed an interest in coming to the UK.'
De Beer has been capped 13 times by South Africa and scored 181 international points.