Forbes Tweedie was born in Ballarat, Victoria, was single when he enlisted with the 6th Battalion, 12th Reinforcement on 10 July 1915 at the age of 18. His unit embarked from Melbourne, Victoria, on board HMAT A40 Ceramic on 23 November 1915. He was wounded in action on 2 March 1917 with a gunshot wound to both shoulders, and was awarded the Military medal for his bravery in the field. He was admitted to hospital in Lewisham and Embarked aboard the Hospital Ship Newhaven at Calais for England on 8 April 1917. From there he embarked for Australia aboard the A 38 on 10 September 1917.

From Commonwealth Gazette No. 133: æ'Pte. TWEEDIE was on duty on Lewis Gun when attack was made. Though severely wounded in neck and back by enemy bomb, he handled his gun quickly and with cool deliberation and accuracy, not leaving his gun till enemy had been dispersed.'
Tree No. 1414