In the quadruple scull at the 2016 Rio Olympics in a crew with James McRae, Karsten Forsterling and Alexander Belonogoff he won the silver medal. In 2019 he was selected with Alex Purnell, David Watts and Caleb Antill to row Australia's quad scull for the 2019 international season. They placed 2nd at the World Rowing Cup II in Poznan and 4th at WRC III in Rotterdam. With Hamish Playfair and Campbell and David Watts, Girdlestone was selected to race Australia's quad scull at the 2019 World Rowing Championships in Linz, Austria. The quad were looking for a top eight finish at the 2019 World Championships to qualify for the Tokyo Olympics. They won their heat and placed third in semi-final, thereby qualifying the boat for the A-final and the Tokyo 2020. They finished in overall world fourth place.