The 28-year-old left-back has signed a three-year contract and joins fellow new boys Adlene Guedioura, Danny Collins and Greg Halford at the City Ground, who all completed moves this week.
“It’s brilliant, I’m really pleased,” Harding told the club's official website, nottinghamforest.co.uk.
“I spoke to the gaffer Sean O’Driscoll and liked what he had to say. I’m really excited.”
Forest chairman Omar Al Hasawi told the club’s official website: “We’re delighted with the way things are taking shape.
“Like Adlene, Danny and Greg, Dan is an experienced performer and knows what it takes to gain promotion from the Championship.”