The 34-year-old former Bolton defender will take the number 24 shirt with the Royals, and is awaiting international clearance to be available for a debut.
Manager Steve Clarke has had his say on the deal with the official club website, which adds to Reading's back-line options after Alex Pearce joined Anton Ferdinand on the injury list, albeit temporarily.
"With the team currently in the middle of a really hectic schedule I felt it was prudent to bring another experienced defender to help share the load. When I heard that Zat was back in the UK and looking for a club I felt he would be a perfect fit. He brings a wealth of experience, good attributes as a defender and good references from previous clubs. It's a sensible deal for both club and player and we look forward to Zat playing his part in helping the team to finish the season on a high note"
Earlier in the week, we wrote this on the defender's then-rumoured capture:
Reading Football Club have a bit of a shortage at the back with summer signing Anton Ferdinand yet to complete a full match for the Royals and only 20-year-old Jake Cooper providing the back-up to first choice duo Alex Pearce and Michael Hector, but that could be about to change if rumours are to be believed.
Former Fulham, Aston Villa and Bolton centre back Zat Knight is interesting Steve Clarke according to the Reading Chronicle, so much so that the massive former England international is set to be in the stands as the Royals take on Brighton at the Madejski Stadium.
The 6 ft 6 in defender was most recently on trial at Championship rivals Watford after an unsuccessful spell at MLS side Colorado Rapids—though having failed to quite convince them, Clarke has now supposedly grasped the opportunity to pounce on the free transfer and add some depth until season's end.
This rumour (if true) doesn't say much for the chances of an Anton Ferdinand recovery any time soon, which makes the decision to sign him look worse with every passing week.
34-year-old Knight made over 350 appearances in the Premier League during his younger years and may well see this as the chance for one final hurrah.
We'd just be happy if he could stay fit, if we're honest.