He turned down a deal last summer, but first division Norwich City dropped their interest following the collapse of ITV Digital - as he is now 24 the Bosman ruling entitled him to leave Glanford Park on a free transfer.
Hull manager Peter Taylor has so far refused to comment on the signing while Iron boss Brian Laws has claimed he knew nothing of a Dawson deal until he went into a board meeting this afternoon.
Northallerton born Dawson has played in 226 games for United, scoring ten times after joining from Nottingham Forest in December 1998 - in a loan move which was later made permanent for £50K.