Lachlan was born at Inverell in 1881, the second child of George and Isabella Walden. He married Ivy South in 1907 and had four children prior to Lachlan's enlistment in 1916. At this time he was living at Gilgai near Inverell and working as a Miner.
Lachlan joined the First Contingent of The Kurrajongs which departed Inverell on 12 January 1916. They spent a short time at the Narrabri Camp before moving to Armidale where he became a member of the 33rd Battalion, C Company. After further training at Rutherford, the Battalion sailed from Australia in HMAT A74 Marathon on 4 May 1916 and arrived at Plymouth, England in early July. Over the next few months the Battalion trained at Salisbury Plain before going to France in November as part of the 3rd Division.
During the Battle of Messines in June 1917, Lachlan received a shrapnel wound to his left eye and was evacuated to King George Hospital in England. As he lost the sight in his eye, he was returned to Australia in September and medically discharged. He was given a pension of three pounds per fortnight, plus thirty shilling per fortnight for his wife and an additional sum for each of his four children. Tragically he died in 1924 and was buried in the Inverell Presbyterian Cemetery.
Private Lachlan Walden's name is inscribed on the Inverell Honor Roll and the Gilgai Honour Roll.