With his club Cill Chartha, McBrearty won a Donegal Minor Football Championship title in 2012.[2] However, he was not fully fit for the final due to a knee ligament injury sustained the semi-final.[3]
First featuring for his county at senior level under the management of Rory Gallagher, McBrearty was first called up ahead of the 2016 season as one of twelve new recruits, alongside such players as Eoghan Bán Gallagher and Stephen McMenamin.[5] McBrearty made a number of appearances during Donegal's Division One campaign in the 2016 National Football League: first he was a second-half substitute in the league opener against Down,[6] then a second-half substitute in the fifth round of fixtures against Roscommon,[7] and then a second-half substitute in the seventh round of fixtures against Monaghan.[8] He also made a substitute appearance in the league semi-final defeat to Dublin.[9]
McBrearty made a substitute appearance for Donegal against Kerry in the opening round of the 2017 National Football League.[10] He made other substitute appearances against Dublin and Tyrone in the third and fifth round of fixtures respectively.[11][12]
Under the management of Declan Bonner, McBrearty scored a point as a second-half substitute against Kerry in Killarney in the opening fixture of the 2018 National Football League.[13] He started the next game against Galway and scored two points.[14] He started the next game away to Dublin and scored a point.[15] He appeared as a substitute in the fourth game against Kildare.[16] He made a second-half substitute appearance against Tyrone in the next game and scored a point.[17] He started the sixth game against Monaghan.[18] He made a substitute appearance in the seventh game against Mayo.[19]
McBrearty did not play in the 2018 Ulster Senior Football Championship final, in which Donegal defeated Fermanagh.[20] He made a late substitute appearance in the preliminary round against Cavan, but featured in neither the quarter-final against Derry nor the semi-final against Down.[21][22][23]
^McNulty, Chris (3 December 2012). "Major show from Eoin McHugh as Kilcar triumph". Donegal News. Retrieved 3 December 2012. Still, this was a performance and a win that they managed with one of their stars, Stephen McBrearty, playing a largely peripheral role due to a knee ligament injury that had forced him off early in their semi-final win over Cloughaneely. McBrearty did get more involved in the closing stages, when Matthew McClean, Cormac Cannon and Man of the Match Eoin McHugh popped over the points that opened the gates of glory for the Towney side.
^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.