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.

Members of the Committee for the Promotion of Virtue and the Prevention of Vice will no longer be permitted to chase suspects or arrest them.
They must instead report observations to security forces personnel.
Religious police officers, who roam the streets enforcing strict standards of social behaviour, are frequently accused of abusing their powers.
Several were reportedly arrested in February for allegedly assaulting (YouTube video) a young woman outside a shopping centre in the capital, Riyadh.
In 2013, four officers were accused of causing a fatal car crash when they pursued two brothers who had refused to turn the radio down in their vehicle. However, a court subsequently acquitted them.
The new law governing the religious police was approved by the cabinet on Monday, but was not published by the official Saudi Press Agency until Tuesday.
Officers will continue to help enforce strict segregation of the sexes, an absolute prohibition of the sale and consumption of alcohol, a ban on women driving and many other social restrictions.
But the new law stipulates that their mission has been amended to "carrying out the duty of promoting virtue and preventing vice in a gentle and humane way, after the model set in this regard by the Prophet [Muhammad] and his rightful successors".
They will also be obliged to display clear identification, showing their names, posts, jurisdictions and official working hours.
The law stipulates that officers will no longer be permitted to pursue suspects, arrest them or ask for identification - only report suspicious behaviour to regular police and anti-drug units, who will decide whether to take the matter further.
Nottingham Forest have signed out-of-favour Hull City winger Thomas Ince on loan until the end of December.
[NEXT_CONCEPT]
The Saudi authorities have moved to curb the powers of the notorious religious police, or "mutawa".