The son of Henry and Annie Grady (née Spooner), Will enlisted in the Army in Whitehall during 1915 when he was 19 years old. He initially joined the 3/1st Battalion, London Regiment (Royal Fusiliers), a Territorial unit that had been formed in January of that year. The 3/1st London Regiment was part of 173rd Brigade within the 58th (London) Division. In June 1916, the battalion was re-designated as 2/1st Battalion, London Regiment when the original 2/1st Battalion was disbanded after seeing service in Malta, Gallipoli, Egypt and France.

Will's battalion moved to France on 20th January 1917 from their base at Sutton Veney near Warminster. He saw action during the German retreat to the Hindenburg Line and at Bullecourt before moving to Belgium on 24th August, being stationed near Poperinghe. The battalion fought in The Salient during the 3rd Battle of Ypres and saw action on the Menin Road Ridge, were involved in the Battle of Polygon Wood and ultimately provided support near Poelcaplle during the final assault on Passchendaele Ridge in November 1917. On the 20th November Will was in 12 Platoon, C Company. At some point in 1917, Will received his two years good conduct award and by this time he was a qualified signaller. On the 29th January 1918, the 2/1st London Regiment was disbanded and Will was posted to 2/2nd Battalion, London Regiment.

In January 1918 the Division moved back to The Somme, initially stationed at Fouencamps near Amiens, before moving east in February where they were positioned near the village of La Fere at the southern end of the British held line. On 21st March of 1918 the German Army launched its last major offensive of the war, the "Kaiserschlacht". The 2/2nd London Battalion were the only battalion of 173rd Brigade in the front line that morning. 6 NCOs and 55 other ranks were killed and over 500 officers and men of the 2/2nd London's, including the commanding officer L/Col Richardson, surrendered to the advancing Germans. A platoon of the 2/2nd London's held out at Travecy Keep until the afternoon of the 22nd March, firing over 18,000 rounds of small arms ammunition and over 200 trench mortars before surrendering. Just 40 men, one NCO and one officer of the 2/2nd London's escaped either death or capture; Will was one of those men. The few remnants of the 2/2nd, 3rd, 2/4th and 8th London's were formed into a composite 'Fusilier Battalion' under the command of Col WRH Dann DSO and Major JA Miller DSO and fought in the retreat across the Crozat Canal and back towards Ambleny, six miles west of Soissons. On the 4th April the 'Fusilier Battalion' was disbanded and on the 6th April the remaining London men entrained from Longpont for Longeau near Amiens. The 2/2nd London's were reinforced during the first two weeks of April and by the 16th their strength was 20 officers and 734 other ranks. On the 17th April the battalion moved into the line at near Hangard Wood and were engaged in improving and strengthening the trenches they took over from 17th Australian Infantry Battalion. At 3am on 24th April, the Germans launched a gas and high explosive bombardment on the 2/2nd London positions followed a tank and infantry attack at 6am. By 9.30am the 2/2nd London's had evacuated their positions and during the day Villers Bretonneux was taken by the Germans which was subsequently re-taken by the Anzac Corps around 10pm that evening. By midnight the remnants of 173rd Brigade re-took Hangard Wood. It was on the 24th April 1918, during the battle in and around Hangard Wood, that William Grady was killed. He was 22 years old.

Will Grady has no known grave and is commemorated on the Pozières Memorial to the Missing, Panel 85.