He was the fifth son of Philip Jacob, Rector of Crawley, Archdeacon of Winchester and Rural Dean, and Anna Sophia, eldest daughter of Gerard Thomas Noel.

His second curacy was at St James's Bermondsey from 1871 until he went to be domestic chaplain to Robert Milman, Bishop of Calcutta in 1872.

Jacob returned to England in 1876, and became examining chaplain to the Bishop of Winchester (Harold Browne until 1891, Anthony Thorold 1891–1895 and finally Randall Davidson from 1896 onwards) for twenty years until 1896.

The latter diocese, which embraced a large part of the poorer outlying parts of London, was large for the effective control of one bishop, consisting as it did of 630 benefices and nearly 900 clergy, and Jacob worked hard to secure the formation of a new bishopric out of it.

[1] Although he emphatically rejected the notion that clergy could serve as combatants, which many sought to do,[2] his diocese provided many army and navy chaplains, and staff for other organisations.