Donnelly was one of several players born in Northern Ireland who benefited from the FAI's attempts to establish their all-Ireland influence.
Together with fellow Ulsterman, Mick Hoy, he made his international debut in a 3–2 away defeat to Norway on 10 October 1937, in a qualifier for the 1938 World Cup.
He made his second appearance for the FAI XI on 18 September 1938 in a friendly against Switzerland and scored the fourth goal in 4–0 win.
The other goal scorers that day were Paddy Bradshaw and Connelly's Rovers teammate, Jimmy Dunne.
Despite getting on the score sheet against the Swiss, Donnelly later lost his place to Kevin O'Flanagan and was released by Rovers shortly afterwards.