The 29-year-old, formerly of Celtic, joins his former team-mate at Oakwell in Reds Manager David Flitcroft.
The attacking midfielder began his career with Foyle Harps before heading to Rochdale where he turned professional, making his Spotland début alongside David Flitcroft in August 2004.
After more than 90 appearances for the Dale, he had spells in Ireland with Shamrock Rovers and Northern Ireland with Derry City before signing for Scottish Premier League giants Celtic in 2008.
In April 2003, McCourt made his senior international bow for Northern Ireland against Spain, as a 74th-minute substitute.