Seymour was gazetted a second lieutenant on the Unattached List in January 1901,[2] before being attached to the Royal Dublin Fusiliers.

In April 1913, Seymour, then of the Royal Dublin Fusiliers, was appointed adjutant of the 25th (County of London) Cyclist Battalion of the London Regiment,[4] in which posting he continued until 1916, before returning to the Royal Dublin Fusiliers to take command of its 10th Battalion.

[8] On 19 March 1949, "having exceeded the age limit", he relinquished his commission as an honorary Colonel of the Devon Regiment on retired pay.

[11] In London on 3 January 1906, he married Edith Mary Parker (d. Maiden Bradley, Wiltshire, 19 April 1962), daughter of William Parker (1816–1893), of Whittington Hall, Derbyshire, England, and Lucinda Steeves (1842–1920), daughter of William Steeves.

Evelyn and Edith had four children: Somerset was a member of The Magic Circle for many years, having first joined it in 1907, after becoming a pupil of the magician Ernest Noakes.