The 30-year-old, who has fallen out with Villa boss Steve Bruce, has joined Forest until the end of the season.
Villa managed to land his replacement up front on deadline day in the form of Scott Hogan from Brentford.
And Bruce will be relieved to have McCormack off his hands, following his issues at Villa Park.
Ross McCormack had fallen out of favour at Aston Villa, resulting in his late departure to Forest
Since his £12million arrival in the summer from Fulham, McCormack has struggled to nail down a starting spot
The manager has questioned the Scotland international's commitment this term and publicly disclosed how he missed training due to his electric gates at home not working.
Since his £12million arrival in the summer from Fulham, McCormack has struggled to nail down a starting spot.
A return to Craven Cottage was mooted earlier this month, but Forest won the race.
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Despite his goalscoring credentials in the Championship, McCormack has only netted three times for Villa and subsequently been allowed to leave until the end of the campaign.
It is not yet known if the forward has a long-term future at Villa Park.
Meanwhile, Midland rivals Forest also secured the signing of Zach Clough from Bolton on deadline day for a fee of £2.5m.