Tonge, whose Elland Road contract is set to expire in the summer, has moved to the New Den on transfer deadline day and could be involved in their home fixture with Huddersfield Town on Saturday.
The 31-year-old has made 12 appearances in all competitions so far this season but has not featured since Boxing Day’s Elland Road 0-2 defeat to Wigan Athletic.
Tonge has been with United for two-and-a-half seasons and was signed permanently from Stoke City in January 2013 by Neil Warnock after establishing himself in the side while on loan.
Tonge scored his first goal for the Whites when he bagged the winner against Bristol City in a 3–2 victory on 29 September 2012.
He was a regular in the side during the 2012/13 campaign, making 39 appearances and scoring five times, before featuring 25 times in all competitions last season.