He enlisted in the First Australian Imperial Force in August 1914 and served in Egypt before landing at Gallipoli, Turkey at the beginning of the campaign.

Keysor remained in Australia until early 1919 working as a clerk in Sydney, New South Wales before returning to England where he began a career in business.

[2] After completing his studies, Keysor travelled to Canada in 1904 where he remained for a period of ten years before emigrating to Australia in 1914 where his brother Stanley and sister Madge were living.

Initially he served in Egypt where the Australians were involved in the defence of the Suez Canal against the Turks, but on 25 April 1915, he landed at Gallipoli where he took part in the subsequent fighting on the peninsula.

Early in the morning on 6 August 1915 the 1st Battalion carried out a diversionary attack at Lone Pine and after heavy fighting that lasted almost the entire day they managed to capture the Turkish trenches.

Over the course of about 50 hours on 7–8 August, Keysor continually risked his life to pick up the Turkish grenades as they were thrown into the trenches and throw them back.

[2][4] Later, despite being wounded and ordered to seek medical attention, Keysor continued to remain in the line, volunteering to throw bombs for another company.

On 28 March 1918 Keysor was wounded and was evacuated from the line before returning to take part in the fighting at Villers-Bretonneux, where he was gassed on 26 May 1918.

[2] In Australia in September 2014 his great niece Keira Quinn Lockyer published his biography "Kyezor VC, Gallipoli's Quiet Hero".