Ireland international caps a perfect deadline day for Wigan Athletic
and live on Freeview channel 276
The 25-year-old, who has six caps for his country, joins for an undisclosed fee on a two-and-a-half-year contract.
During his time at Dundalk, McGrath also worked under Latics CEO Mal Brannigan.
McGrath joined St Mirren in January 2020, since when he's made 79 appearances, scoring 20 goals, and is the club's reigning Player of the Year.
Get 20% off our sports subscription package and stay up to date with all the latest Wigan Athletic news with a year’s subscription to WiganToday for less than 9p a day. Use promo code TRANSFER20