Kilgallon is available on a free transfer after seeing out his contract at Blackburn earlier this summer.
A number of clubs have shown an interest in the central defender, but Bradford have moved quickly to agree a deal for Kilgallon.
The 32-year-old, who came through the ranks at Leeds United, has made over 300 first-team appearances in his career to date and captained Blackburn in the 2014/15 season as they reached the FA Cup quarter-finals.
Bradford boss Stuart McCall is in the market for a new defender after losing last season's player of the year Reece Burke following the end of his loan spell from West Ham United.
McCall is a big admirer of Kilgallon having worked with the defender during his time as assistant manager to Neil Warnock at Sheffield United.
McCall sees Kilgallon's versatility and experience as a key addition to his squad for the upcoming season as he looks to build a side capable of winning promotion to the Championship.