The prop, who was part of the Scotland 'A' squad at the IRB Nations Cup in June 2010, has long been tipped for a career at the top and received the prestigious John Macphail scholarship in 2009.
Niven, who was in the Trinity Academy first XV for three seasons before progressing to Edinburgh Accies, played at tighthead in all of Scotland's matches in the 2008 under-20 Six Nations Championship.
He made his debut in the France game at Falkirk, and scored a try against England at the same venue.
In June 2008, he played in three games in the IRB Junior World Championship in Wales.
In 2007, he played for Scotland in the IRB under-19 world championship in Belfast and was a member of Accies' squad for the Scottish Hydro Electric Cup Final against Glasgow Hawks.