Coombes was named as a core member of the Scotland 7s squad for the first time ahead of the 2018/19 season.
He made his first appearance on the World Series in January 2018, receiving a call-up for the Sydney Sevens after impressing for London Scottish.
A former Scotland U20 international, Coombes was a member of the 12 man squad for the 2018 Sevens World Cup in San Francisco.