Born in Castlebar, County Mayo, McStay was introduced to the game by his father, a former player with Tuam Stars.
[citation needed] McStay made his debut on the inter-county scene at the age of sixteen when he first linked up with the Mayo minor team.
[citation needed] McStay retired from inter-county football after breaking his leg while playing against Castlebar one week after Mayo's exit from the 1990 championship.
[5] As a member of the Connacht inter-provincial team on a number of occasions, McStay never won a Railway Cup medal.
As a club manager he steered Roscommon Gaels to championship success in 2004, before guiding St Brigid's to the All-Ireland title in 2013.
[8][9] He led the Roscommon team that won the 2017 Connacht Senior Football Championship, beating Galway 2–15 to 0-12, in Pearse Stadium, Salthill.
[10] McStay got himself into bother while his team were playing Donegal in the 2018 Championship, involving himself in a number of different incidents with match officials, shoving a linesman in a chest and hurling a football at full force in the direction of another.
[13] He applied for the Mayo managerial vacancy in 2014 but was surprised when Pat Holmes and Noel Connelly became joint managers ahead of the 2015 season.
People I knew, that I had had played with, was on panels with, were saying publicly that they had no interest in the job and were actually talking about the position while I thought in my head that I was actually crossing Ts and dotting Is.
[16][17] In 2002, McStay commented on Mayo's lack of clinical finishing and tendency to amass high wide tallies in games: "We are not clever up front, we haven't been for 30 years and I would include my own vintage.