"We're naturally very pleased to confirm Taine's signature today [Sunday]," said Sinderberry on his club's official website. "And we're delighted that he has decided to begin the next phase of his career at the club."
Randell, the youngest-ever All Black skipper, has won 51 Test caps, but has featured sparingly under current national coach John Mitchell, who this year has ignored the claims of Randell, fullback Christian Cullen, first five-eighth Andrew Mehrtens and another former skipper, hooker Anton Oliver.
Not only has Randell, who earlier this year stepped down from the New Zealand Maori squad, captained his country, but he has leadership experience at Super 12 and NPC level, while he also captained the Barbarians in their recent matches against England, Scotland and Wales.
As an added bonus, Randell can also play in any back row position.
The 28-year-old Randell saracens.com that he was delighted at joining the Vicarage Road-based club: "I'm very excited about the next phase of my career and can't wait to get settled in at the club.
"I know how ambitious the club is and I am looking forward to playing my part in getting the club back to where they belong."
Randell will join former Wallaby and Leicester inside back Rod Kafer in the Saracens playing ranks, along with France hooker Raphael Ibanez, Fiji fly-half Nicky Little, Argentina prop Emiliano Bergamaschi, Fiji lock Simon Raiwalui and England second rower Alex Codling.
"Taine's signature brings an end to activity in the transfer market and we're now confident that we have a squad that can take the club forwards over the next few seasons," said Sinderberry.