Born in Skibbereen, Cork, Coombes first began playing rugby for his local side Skibbereen RFC alongside his cousin, Gavin Coombes, before playing schools rugby for Christian Brothers College during his leaving cert cycle and winning the Munster Schools Rugby Senior Cup in March 2016 alongside Munster teammate Alex McHenry.
[2] He made his first non-competitive appearance for Munster in their 32–28 pre-season friendly victory against London Irish on 17 August 2018.
[3][4] Coombes made his full senior debut for Munster in their 2018–19 Pro14 fixture against South African side Cheetahs on 4 November 2018, having been drafted into the starting XV late on after Sammy Arnold failed to recover from concussion, and scored his first try for the province in their 30–26 away win.
[5] Coombes joined the Munster senior squad on a one-year contract ahead of the 2020–21 season[6] and extended that deal by a further year in February 2021.
[8] Coombes was called up to the Ireland Under-20 squad for the 2017 World Rugby Under 20 Championship after an injury suffered by fellow Munster colleague Colm Hogan,[9] and he went on to start against New Zealand Under-20.