The left-back arrived from Blackpool on a month's deal on Thursday to cover the absence of the injured Laurie Wilson, but that could be extended if things go well at New York.
"We decided it would be good for me to get some games with the Millers," 25-year-old Harris told the club's official website. "If I'm not going to be playing at Blackpool then I'd be looking to extend the deal, it would clearly benefit me and both clubs.
"I'm looking forward to coming and doing my best for Rotherham.
"The manager likes to play in the right way. I like to get forward and get to the byline when possible and I scored a few set-pieces when I was playing in Scotland.
"At the end of the day if I can help Rotherham win some games, then that is the important thing."