Oldisworth’s grandfather settled at Poulton, five miles from Cirencester. His father, ‘in Queen Mary’s days a colonel in Flanders’,
Although he took up residence in St. Martin-in-the-Fields after his marriage, Oldisworth probably had family connections with Cirencester, for which borough he was returned in 1604. Oldisworth is mentioned only twice in the records of the first session. In his sole recorded speech he moved, on 27 Apr., for a new writ for Gloucestershire on the death of Sir Richard Berkeley, and on 4 July he was named to the committee for the bill to confirm letters patent.
In the third session Oldisworth was named to 13 committees and was instructed to help with the Lords about the Union (24 Nov. 1606).
Oldisworth was named to five committees in the fourth session, including those for bills against forcible entry (24 February), to enforce the payment of debts due by simple contract (27 June) and to confirm the title of contractors for Crown lands (5 July).
In 1595 Oldisworth had been granted the office of clerk of the hanaper in reversion to Henry Sadler*.
In 1611 Oldisworth was able to provide a dowry of £1,000 on the marriage of his daughter to Alexander Baynham.
