His older brother, Johnny, a graduate of Trinity College Dublin, played rugby union for Ireland at schoolboy and university levels.

[1][2][3] In 2002–03, together with Mark Gleghorne, Watt was a member of the Royal Belfast Academical Institution team that won the Burney Cup and finished as runners-up in the All Ireland Schoolboys Hockey Championship.

In 2003–04, together with Mark and Paul Gleghorne, Watt was a member of the Instonians team that won the Irish Senior Cup, defeating Cork Harlequins 1–0 in the final.

[6] Between 2005 and 2009, while attending Heriot-Watt University, Watt played for Grange in the Scottish Hockey National League.

[1][4] In 2008–09 Watt scored 17 goals for Grange, including two in the Scottish Hockey Cup final as they defeated Inverleith 4–0.

[17] In 2015–16, along with Jonathan Bell, Sean Murray and Paul Gleghorne, Watt was a member of the Lisnagarvey team that won the Men's Irish Hockey League and the EY Champions Trophy.

[20][21] Watt and Lisnagarvey also reached the final of the Irish Senior Cup but lost to Monkstown after a penalty shoot-out.

[4][26][27][28] In his first major tournament, the 2008 Men's Field Hockey Olympic Qualifier, he scored twice in the opening 4–0 win against France.

[31] Watt was also a member of the Ireland team that won the bronze medal at the 2015 Men's EuroHockey Nations Championship.