The 26-year-old is the club's fifth signing of the window and joins fellow wing-back Peter Kioso, central defender Jamie McCart and forwards Tom Eaves and Conor Washington at the New York Stadium.
The Millers have lost two key men this summer with Michael Smith and Michael Ihiekwe declining new deals to sign for Rotherham's South Yorkshire rivals Sheffield Wednesday.
Paul Warne's side were automatically promoted from the third tier last season and will be aiming to avoid another relegation from the Championship, after dropping out of the second tier in the last two campaigns they have played in it.
Across Yorkshire, Hull City's latest arrival came in the shape of Portuguese centre-back Tobias Figueiredo on Tuesday.
The Tigers lost George Honeyman this week as the player's move to Millwall was completed while the club have rejected an offer from Brentford for Keane Lewis-Potter.
With two months remaining of the transfer window there is still plenty of time for Hull and Rotherham to get more business done. The Yorkshire pair are among the favourites for relegation and we have put how the final 2022-23 Championship table will look based on the bookmakers' odds for relegation...
1. Watford - 66/1
The Hornets were relegated from the Premier League last term but are not expected to be dragged into another survival battle in the Championship but rather challenge for an immediate return to the top flight. Photo: Getty Images
2. West Brom - 33/1
The Baggies are tipped to be among the promotion contenders despite a disappointing 10th-placed finish last term. Photo: Getty Images
3. Norwich City - 66/1
The Canaries finished bottom of the Premier League last term and are tipped to fight for a place back in the top flight. Photo: Getty Images
4. Sheffield United - 33/1
The Blades missed out on promotion last season after being knocked out in the play-off semi-finals by Premier League-bound Nottingham Forest. They are tipped to challenge at the top end of the table again. Photo: Getty Images