Johnston was part of the 2015 Rockwell College side that claimed the Munster Schools Senior Cup. Having previously represented Munster U18 Schools, the Clonmel native also captained Ireland U18 Schools during the Rugby Europe U18 Championship in France earlier this year.
Joining the Munster sub-academy ranks at the beginning of season 2015/16, the young fly half won inclusion - alongside his older brother and academy player David - in the Munster senior squad for all three pre-season encounters, starting the final game against London Irish.
The following month the Garryowen man played his part in Munster U20s' Interprovincial success and was added to the full academy programme in November.
After recovering from a shoulder injury sustained in action for Ireland U20s against a Munster Development XV in December, Johnston won inclusion for Ireland at the 2016 World Rugby U20 Championship in Manchester.
The playmaker started the opening two games, including the first ever win over New Zealand by an Ireland men's side. Unfortunately, that same win saw Johnston sustain another shoulder injury which ruled him out of contention for months.
Johnston returned to action in the British & Irish Cup for Munster in December 2016 and made three appearances for the Ireland U20s in the 2017 Six Nations.
Played his part in Munster A's B&I Cup title-winning campaign, but a fractured fibula sustained in the semifinal win over Ealing Trailfinders ruled him out for the final and the impending 2017 World Rugby U20 Championship with Ireland.
Progressed to a Senior Development contract at the beginning of the 2017/18 season after completing two years of the Greencore Munster Academy programme.
The playmaker was given his Munster debut in March 2017 and made 12 senior appearances, scoring 29 points before he signed a deal with Ulster for the 2019/20 season.
He was yet to score a try in the 2019/2020 season however he had added 37 valuable points with his boot.
|2019 - present|
|2016 - 2016|
|2016 - 2019|