From leaving school, Farndale signed as an EDP with Edinburgh Rugby, where he became and is still the youngest ever debutant for the club.

He became a mainstay of the international under-20 side from an early age, featuring in no fewer than three IRB Junior World Championships (2012, 2013 and 2014).

A leg break in October marred his attempts to add to his first senior competitive appearance in the last match of the 2011–12 season against Cardiff, however he returned in time for the 2013 World Championships in France, before going on to join the all-time leader board in 2014.

He co-captained Scotland in 2018/19 with Robbie Fergusson before taking over the captaincy in 2019 until the Scottish program moved to a Great Britain setup.

Farndale captained Scotland at the 2022 Rugby World Cup Sevens in Cape Town.