In April 1917 during the Battle of Vimy Ridge, he received a through-and-through bullet wound from a machinegun in his arm and was temporarily invalided to England.

On 26 October 1917 near Passchendaele, Belgium, he performed a deed for which King George V awarded Holmes the Victoria Cross: "when the right flank of the Canadian attack was held up by heavy machine-gun fire from a pill-box strong point and heavy casualties were producing a critical situation, Private Holmes, on his own initiative and single-handed, ran forward and threw two bombs, killing and wounding the crews of two machine-guns.

Sergeant Tommy Holmes, VC, returned to Owen Sound after the war to great fanfare and receiving a hero's welcome.

“For most conspicuous bravery and resource when the right flank of our attack was held up by heavy machine-gun and rifle fire from a ‘pill-box’ strong point.

Holmes, on his own initiative and single-handed, ran forward and threw two bombs, killing and wounding the crews of two machine guns.

His memorial service was attended by Victoria Cross recipients Henry Howey Robson, Colin Fraser Barron and Walter Leigh Rayfield.

Of significance is that two other VC recipients are also buried at Greenwood Cemetery, Air Marshal Billy Bishop and Major David Vivian Currie.

A replica of Thomas Holmes VC medal is now on display at the Owen Sound Royal Canadian Legion Branch #6.