As a youth, McGonagle played as a goalkeeper.[1]Declan Bonner called McGonagle into his development squad but by the 2013 McGuigan Cup (Ulster Under-17) Final, McGonagle had moved outfield.[1]
First featuring for his county at senior level under the management of Rory Gallagher, McGonagle was first called up ahead of the 2016 season as one of twelve new recruits, alongside such players as Eoghan Bán Gallagher, Stephen McMenamin and Ciarán Thompson.[3] McGonagle played twice during Donegal's Division One campaign in the 2016 National Football League, featuring in the first and last fixtures, both times as a substitute: first he made a late appearance in the league opener against Down,[4] then he came on in the league semi-final defeat to Dublin.[5]
McGonagle made a substitute appearance in the 2018 Ulster Senior Football Championship preliminary round defeat of Cavan but made no further appearances in the competition as Donegal secured the Anglo-Celt Cup.[11][12][13][14]
McGonagle started against Clare in the opening fixture of the 2019 National Football League in Ennis, scoring one point from a free.[15] He scored the only goal of the game against Meath in the second fixture.[16] He started the third, fourth, fifth and sixth fixtures against Tipperary, Fermanagh, Armagh and Cork.[17][18][19][20] He started the seventh fixture against Kildare, scoring one point.[21] Donegal qualified for the National Football League Division 2 final and McGonagle started the game as Donegal defeated Meath to win the title.[22] McGonagle had featured in a lot of matches during the 2019 National Football League. Then he sustained an injury.[23]
McGonagle started Donegal's first fixture of the 2020 National Football League against Mayo and scored a point.[24] He did not participate in the second game against Meath.[25] He later started the third, fourth and fifth games against Galway, Dublin and Monaghan respectively.[26][27][28] Then the COVID-19 pandemic brought play to a halt. Play resumed behind closed doors on 18 October with a home game against Tyrone; McGonagle started that game and scored a point.[29] He also started and scored a point in the concluding game of the league campaign away to Kerry.[30]
McGonagle made his first championship start against Tyrone in the 2020 Ulster Senior Football Championship quarter-final.[31] He also started the semi-final victory against Armagh, scoring two points (including one mark), and the final against Cavan, in which he scored two points.[32][33]
McGonagle started each of Donegal's four fixtures of the 2021 National Football League, against Tyrone, Monaghan, Armagh and Dublin, scoring one point each against Tyrone and Monaghan and two points against Dublin.[34][35][36][37] He started each of Donegal's three fixtures in the 2021 Ulster Senior Football Championship, scoring two points against Derry in the quarter-final and a goal against Tyrone in the semi-final.[38][39][40]
McGonagle started Donegal's first two fixtures of the 2022 National Football League, against Mayo and Kildare.[41][42] He did not play in the third game, against Kerry,[43] nor in the remaining fixtures against Tyrone, Monaghan, Dublin and Armagh.[44][45] He made a substitute appearance against Armagh in the 2022 Ulster Senior Football Championship quarter-final and followed this with a temporary substitute appearance (for Hugh McFadden) against Cavan in the semi-final (during which he scored a point).[46][47] He started the final against Derry (which included extra-time, during which he was substituted).[48] He also started the 2022 All-Ireland Senior Football Championship qualifier loss to Armagh, standing in as goalkeeper for a penalty kick when Shaun Patton was shown a black card.[49]
^ abcdefghiFerry, Ryan (10 June 2021). "McGonagle keen to keep hold of a starting jersey". Donegal News. In his early teenage years it was thought he might be more of a replacement for Paul Durcan than Rory Kavanagh. In fact when he was first called into the development squad by Declan Bonner it was on the premise of playing as a goalkeeper. Bonner can't even remember if he saw McGonagle in action between the sticks… After working as a PE and Maths teacher in St Eunan's College over the last nine months, he is now on his summer holidays, and will use the spare time to help his recovery between training sessions and matches… The 25-year-old will have to be on his game this weekend as he could be asked to track the runs of Brian Fenton, Brian Howard, or James McCarthy. Details are from the print edition, published on the same date as "Donegal's McGonagle keen to keep hold of a starting jersey".
^Maguire, Gerry (24 November 2015). "Rory Gallagher puts his faith in youth with minor promotions". The Irish News. Retrieved 24 November 2015. The new players on the squad are Danny Rodgers (Dungloe), Stephen McMenamin (Red Hugh's), Kieran Gillespie (Gaoth Dobhair), Michael Carroll (Gaoth Dobhair), Eoin Bán Gallagher (Killybegs), Ciarán Thompson (Naomh Conaill), Stephen McBrearty (Kilcar), Caolan McGonigle (Buncrana), Jack O'Brien (Naomh Muire), Tony McClenaghan (Moville), Rory Carr (St Eunan's) and Caolan Ward (St Eunan's). With the exception of Ward, all of the above are in the 19–20 age bracket.
^O'Brien, Kevin (22 November 2020). "As it happened: Donegal v Cavan, Ulster senior football final". The42.ie. Retrieved 22 November 2020. 16 mins — Ryan McHugh swivels and points, before Caolan McGonagle adds another… 63 mins – McGonigle[sic] levels the game with a pressure point. We're in for a thrilling final 10 minutes now.
^Ferry, Ryan (19 November 2020). "Ryan takes a look at the key battles ahead of Sunday's Ulster final". Donegal News. p. 59. Caolan McGonagle… will be a key player for Donegal on Sunday… He also brings huge workrate and the St Eunan's College teacher is happy to carry possession for his team.
^"Seven county players gain Gaelic Life awards". Donegal News. 16 January 2020. p. 73. ... Anthony Thompson, Ciaran Thompson from Naomh Conaill along with Buncrana's Caolan McGonagle were all named on the football team. The Thompsons and Caolan McGonagle were unable to attend the event though their awards were collected in their absence.