The 22-year-old only joined the Tigers from Blackpool in the summer.
But he has been limited to four games for the Premier League side and has not appeared in the league since August.
Reds boss Stuart Pearce told BBC Radio Nottingham: "He needs first-team football and a challenge. He's not featured much for Hull, so this move - for him and us - will be fantastic."
Chairman Fawaz Al Hasawi said on Twitter: "I'm thrilled to say Thomas Ince has joined us on loan until 28 December. A very warm welcome."
England Under-21 international Ince is the son of ex-England and Manchester United midfielder Paul Ince, and also made eight appearances for Forest's neighbours Notts County in 2010-11.
Nottingham Forest have signed out-of-favour Hull City winger Thomas Ince on loan until the end of December.