The 28-year-old goal-kicking Waikato Chiefs and Bay of Plenty playmaker has initially signed a one-year deal with the Men In Black. He will join Saracens in October following the end of his NPC commitments with Bay of Plenty.
Saracens Head Coach Rod Kafer said: "We are delighted that Glen will be joining us next season. He is a very skilful player, an excellent goal kicker and meets our recruitment criteria.
"He is in the right age bracket and brings with him a wealth of experience from the Rebel Sport Super 12 and Air New Zealand NPC competitions. He's not had the international recognition we feel a player of his quality deserves, but that may be something he addresses while with us.
Kafer added: "Initially he has joined us on a one-year deal but we are hopeful that we will have the opportunity of extending this further."
As one of the most experienced players in the Waikato line-up, Jackson played an important role in the team which lost out in this year's Super 12 semi-finals to the eventual champions the ACT Brumbies. His 59 appearances for the Chiefs since his debut in 1999 have brought him a points haul of 479.
More recently, Jackson was part of NZ Moari side that beat England in the final of the Churchill Cup. He also played for New Zealand Barbarians at Twickenham in December 2003 when he came face to face with Richard Hill, then captaining the England side in their first match since their World Cup victory.