Cardiff will allow long-serving Kevin McNaughton to leave this summer along with Danny Gabbidon and Nicky Maynard.
Highly-rated Atletico Madrid midfielder Saul Niguez has signed a new five-year contract.
Both clubs expect the necessary paperwork to be completed on Friday morning in time for the 29-year-old to make his Town bow against Peterborough on Saturday.
Tabb has been pushed down the pecking order at the Madejski Stadium since the Royals' promotion last term, featuring just 12 times in the top flight.
The January acquisitions of Daniel Carrico and Hope Akpan have seen Tabb marginalised further and he will now set his sights on lifting Mick McCarthy's Ipswich up the table.
The Tractor Boys are only four points above the relegation zone and Tabb's arrival comes at a crucial time with fellow midfielder Lee Martin set to start a three-match suspension.