He has the task of mentoring those selected and attempting to guide them towards victory in the competition, the first for an over-25 entrant since Steve Brookstein's win in the first series in 2004.
The Sun reports that Simon Cowell personally rang the judges and assigned them their categories.
Louis Walsh has the Groups category, Tulisa Contostavlos will be mentoring the Girls and Nicole Scherzinger will look after the Boys.
A source close to the star reportedly said: "Gary doesn't like joke acts and the Overs category is often full of novelty acts. In the past, when Louis has mentored them, the public got used to jokey acts like Wagner Carrilho and Johnny Robinson.
"Gary is preparing himself for an uphill battle."
The next series of The X Factor is also set to feature a number of acts who are returning to the competition, including Jade Richards and Sian Phillips.
Watch Gary Barlow on last year's series of The X Factor below: