Kyrle Nalder Stephens was born in Hendon, Middx in 1881, the eldest son of Arthur Nalder Stephens (Stockbroker) and his wife Maria and baptised on 13 November 1881 at St Mary's, Hendon. On the 1891 Census, the family were living with Kyrle's widowed grandmother at Fair View, Sunny Gardens, Hendon with 3 servants.
He was educated at Philberds, Maidenhead and at the Choleley School, Highgate. After leaving school he joined the firm of B M Clarke & Co, where his father was a partner. He was elected a member of the Stock Exchange in 1904 and on the death of B M Clarke in 1910 he became a senior partner.
On 1st August 1902 he was admitted to the Freedom of the City of London, by redemption, in the Company of Leathersellers when he was a Stockbroker's Clerk. He married Rose Mildred Kempster on 2 June 1906 at St Mary's , Hendon, Middx and in 1911 they were living Dormie Cottage, Radlett Park Road, Radlett, Herts, with their two children, and he was working as a Stock Broker.