Private Andrew Walker was born in the Parish of St. George's, Paisley and attested for the Medical Staff Corps at Glasgow in November 1855, aged 26 years. Following stints of duty at Scutari and in China as a 2nd Class Orderly, he transferred to the Army Hospital Corps as a Private in April 1860. Diagnosed as 'Unfit for further service due to chronic dysentery' in April 1862, he was duly discharged at Chatham.