[citation needed] He progressed to a centrally held Scotland 7s contract in the summer of 2011 before being approached to join the Edinburgh Rugby elite development programme, after a string of impressive showings in the back-row.

After impressing for Edinburgh Rugby, Watson made his international debut in the home defeat to Italy during the 2015 Six Nations Championship.

[4][5][6][7] Watson was selected in Scotland's squad for the Rugby World Cup in 2019, but suffered a tournament-ending injury in the opening match against Ireland.

[12][13] After performing well in the tour's warm-up matches, he was selected on the substitutes' bench for the first Test, coming on early in the second half as the Lions won 22-17 to lead the series.

[14][15] as of 1 October 2023[update] Watson has gained two nicknames from fans: "The Mish", a shortening of his given name, and "Pinball", in reference to his unique running style which sees him bounce off several players over a short distance whilst carrying the ball.