Born in 1813 into a well-off middle-class family in Shromell, west Tipperary, Sadleir was educted at home by private tutors and received his second level education in Clongowes Wood College. Sadleir’s maternal relatives, the Scullys of Kilfeacle, were wealthier than the Protestant Sadleirs and his grandfather, James Scully, amassed a fortune in land and money.

Sadleir established a law firm in Great Denmark Street, Dublin where he gained experience in business and land transactions. He was a key figure in the foundation of the Tiperary Joint Stock Bank which eventually became known as Sadleir’s Bank. He moved to London in 1846 and quickly established himself as an astute buisnessman and legal advisor to railway speculators. He invested in railway companies in England and Europe and became chairman of the Royal Swedish Railway Company.

The key to his advancement lay in political power and in 1847 Sadleir became M.P. first for the borough of Carlow then Sligo. His political future seemed assured when he became a Junior Lord of the Treasury in the Aberdeen ministry in 1852 but from 1853 onwards his career was blighted by political scandals. When his financial position began to deteriorate in 1855 he resorted to massive fraud and embezzlement even defrauding family and friends. When his crimes could no longer be hidden the 43 year old Sadleir poisoned himself on Hamstead Heath on 16th Feruary 1856.