Boss Paul Warne had tried to sign the 25 year old defender last season, but was unable to due to technicalities.
Raggett joined Norwich last summer from Lincoln, (where he was sent back on loan to) but has found himself down the pecking order at Carrow Road.
Norwich boss Daniel Farke told Norwichs official club website; “Sean is not 18 or 19 anymore. He needs game-time and we’ve found a solution that he’s able to play at our level and with a club which doesn’t necessarily have as much competition in the centre-back position.”
Raggett joins the Millers on a season loan, but NOrwich have the option to recall him in January.