The tenacious midfielder spent some of last term with Peterborough and has joined a team battling it out with Posh and several other sides in the bid to avoid relegation to League One. He will wear the no.28 shirt.
David Flitcroft's Tykes have been in incredible form of late, winning eight of their last nine league and cup fixtures, and the 20-year-old is sure to provide more steel in the middle of the park.
Tunnicliffe has been a regular in the Under-21s for United, scoring once (against Sunderland), and is available for the weekend encounter at Bristol City and, intriguingly, the FA Cup quarter-final tie against Manchester City next month.
The former Jimmy Murphy Young Player of the Year made his first-team debut for United in the Capital One Cup tie against Newcastle and also came off the bench during the 5-4 defeat to Chelsea in the following round.