The centre-back, 26, has not played for the Bluebirds since missing a penalty in City's Carling Cup final defeat to Liverpool in February.
He was also left out of Championship Cardiff's pre-season tour by manager Malky Mackay.
Gerrard, cousin of Liverpool and England captain Steven, joined Cardiff from Walsall in 2009 and spent the 2010-11 campaign on loan at Hull City.
The former Everton trainee is the latest of a string of acquisitions by Town manager Simon Grayson as he prepares the newly-promoted Terriers for life in the Championship.
