Coulter made his inter-county debut for Armagh at the age of 17 in 2005.[2] He won his first Nicky Rackard Cup in 2010.[citation needed] He won his second Nicky Rackard Cup with Armagh in 2012, scoring 2–2 in the final against Louth.[9] He continued to play for Armagh until 2016.[2]
Coulter began playing for Donegal in 2017.[2] He played for Donegal during the 2018 National Hurling League, when the county recorded their first competitive victories over Derry and Down (he scored 1–1 in the comprehensive defeat of Derry and 0–2 in the three-point defeat of Down).[3][10][11] Donegal also defeated Armagh in the closing game of that league campaign, with Coulter contributing 2–1 (including one penalty) to the three-point victory over his former side.[12] Donegal went on to win the 2018 Nicky Rackard Cup, Coulter's first for Donegal and third overall, with Coulter scoring 1–10 (0–4 of which were frees, 0–1 of which was a '65) in the final, a seven-point victory for Donegal.[13] He was later named Nicky Rackard Hurler of the Year.[14] He and fellow Donegal player Stephen Gillespie featured on the Nicky Rackard Team of the Year.[14]
Coulter was named as a replacement on the 2018 All-Star team for their game against the 2019 All-Star team in Abu Dhabi in November 2019.[15][16] He put in a man of the match performance and scored 1–6 from play, despite not being an actual All-Star and being in the presence of hurlers from teams ranked above any across Ulster.[16][17][15]Martin Breheny, in the Irish Independent, wrote that Coulter, having outscored teammates of the calibre of Séamus Harnedy (Cork) and Graeme Mulcahy (Limerick), had "made a major statement on behalf of hurlers from lower-ranked counties".[18]
^ abcFerry, Ryan (7 May 2020). "Coulter is March Sports Personality of the Month". Donegal News. p. 54. However the Dromore NS teacher did receive a boost late last year when he was selected to go on the All Star trip to Abu Dhabi. Original print title was "Coulter collects league title in Carrickmore".
^ abcd"Declan Coulter shines in PwC All Star game in Abu Dhabi". Highland Radio. 30 November 2019. Retrieved 30 November 2019. It was a great experience being from one of the weaker counties and a nice honour. It was about two weeks ago that I got notice so it was a matter of trying to arrange work and baby sitters but it was a trip you couldn't turn down – and for my wife Ciara as well to get something out of it.