Osborne’s grandfather and namesake, a younger son from Essex, founded his family’s fortune by obtaining an Exchequer office - that of lord treasurer’s remembrancer - which became hereditary. He bought Chicksands in 1576, and sat in seven Elizabethan Parliaments. Osborne’s father, Sir John, nearly matched this record, participating in six sessions.
Osborne was returned for Corfe Castle in 1624, perhaps on the recommendation of one of the borough’s previous Members, Sir Thomas Hatton, who was later one of his trustees.
In 1628 Osborne succeeded his father as treasurer’s remembrancer, but he continued to spend most of his time on Guernsey. Upon the outbreak of the Civil War, he held Castle Cornet for the king, but in 1646 he handed over command to (Sir) Thomas Fanshawe II*, and went into exile in France. He compounded for his delinquency in 1650, paying £3,737.
