He was an unused substitute throughout the National League, Leinster Championship and All-Ireland Championship campaigns. On 27 January 2018, Donnelly made his first appearance for the Kilkenny senior team. He was introduced as a 43rd-minute substitute for Conor Martin in a 1-24 to 0-24 defeat by Cork in the National League. On 8 April 2018, Donnelly was selected at left wing-forward when Kilkenny faced Tipperary in the National League final. He scored two points from play and collected a winners' medal following the 2-23 to 2-17 victory. Donnelly was selected on the bench when Kilkenny faced Galway in the Leinster final on 1 July 2018. He was introduced as a substitute for Richie Leahy in the 0-18 apiece draw. Donnelly broke onto the starting fifteen at right wing-forward for the replay a week later, however, he was substituted by Luke Scanlon in the 1-28 to 3-15 defeat. On 30 June 2019, Donnelly was listed amongst the substitutes when Kilkenny faced Wexford in the Leinster final. He remained on the bench for the entire game which Kilkenny lost by 1-23 to 0-23.