The 34-year-old centre-half has signed a one-year deal at New York Stadium following his release from fellow Championship club Nottingham Forest at the end of last season.
Collins made eight appearances for Forest last term, but has a wealth of second-tier and Premier League experience, having joined Stoke for £2.75million in 2009.
His arrival brings vital presence to the Millers' defensive ranks following the exit of Craig Morgan and Kari Arnason, joining Kirk Broadfoot and Richard Wood as specialist centre-halves at boss Steve Evans' disposal.
The Millers boss delighted to get a man with such experience.
“The opportunity to sign Danny came up after I became aware that he’d been in negotiations with two other Championship clubs and we met up with him and had a chat,” he said.
“His references were impeccable in terms of his fitness, hunger and desire it all shone like a beacon of light in the ocean and that attracted me to him.
“We’ve had a wonderful opportunity to bring him in for a year with the option of extending that if Danny proves to be as good as I think he can be.
“The main thing is that he’s hungry and he likes what we’re trying to do here so he’ll come in and play a major part.
“He’s big, he’s strong and he’s aggressive and quick. He talks well and he can organise the defence so he will be a very good addition.
“I got the benefit of being able to watch him live a couple of times for Forest last season and he was simply outstanding."
Collins joins Aidy White, Emmanuel Ledesma, Lewis Buxton and Joe Mattock through the arrivals door at New York.
