Clarke was the eldest son of
Sir Edward Clarke of St. Vedast's, London,
Lord Mayor of London, and his second wife Jane Clutterbuck, daughter of Richard Clutterbuck. He was admitted at
St Catharine's College, Cambridge on 20 March 1689 and at
Middle Temple on 17 March 1690. He married Elizabeth Pinfold, daughter of Alexander Pinfold of Hoxton, Middlesex on. 9 January 1699. Clarke may be the ‘Thomas Clerk’ who was named with his brother-in-law,
Maynard Colchester as one of the founding members of the
Society of the Propagation of the Gospel in 1701. They had both been educated at the Middle Temple and shared an interest in landscape gardening. In 1703 he succeeded his father to Brickendon, and assumed the role of a county country gentleman. In 1704 he became Freeman of Hertford. He carried out charitable works in his neighbourhood among which he ‘built a gallery in the church, set up chimes in the steeple, put 90 poor children to school, gave bibles, catechisms etc., and distributed half-peck loaves and two oxen among the poor at Christmas’. ==Career==