The 24-year-old joined the club on Friday, initially on an emergency loan deal which Millers manager Steve Evans revealed would be turned into a full-time move at the start of the week.
Bradford-born Ward, who can also play in a central attacking role, has signed a two-and-a-half year contract.
The Bradford-born player, who had reportedly also been interesting Leeds United, made his debut in Saturday’s 1-0 defeat at Brentford along with his Huddersfield team-mate Adam Hammill.
Liverpudlian Hammill has signed for the Millers on loan for the rest of the season with a view to a full-time move if all goes well.
Evans, also keen on bringing in a striker, said of Ward: “There was a time when we thought Danny Ward was heading to our Yorkshire neighbours Leeds United, but thankfully we were able to move very prudently with our chairman backing it.”
The Millers also hope to sign defender Scott Wootton – who has returned to Leeds after his loan spell expired on Saturday – on a full-time basis.
The clubs are understood to be in talks about arranging a full-time switch with the former Manchester United defender having impressed during his time in South Yorkshire with the Millers.
Febian Brandy, who recently left Rotherham, has signed a deal at Rochdale for the rest of the season.
Brandy, 25, who also had an unsuccessful spell in Yorkshire at Sheffield United, made just one substitute appearance for the Millers following his summer arrival – before being loaned out to Crewe – in the 2-0 home loss to Brentford on August 30.
York City have extended Bournemouth defender Stephane Zubar’s loan at the club until the end of the season.
The 28-year-old has made 10 appearances since joining the Minstermen.
However, he is unavailable until the home game with Dagenham & Redbridge on February 7 following his sending-off against Plymouth Argyle earlier this month.
That dismissal incurred a four-match ban as it was his second red card of the campaign.