Oldisworth was the son of Arnold Oldsworth and his wife Lucy Barty daughter of Francis Barty of Antwerp. He was a fellow of Magdalen College, Oxford, and became secretary to the 3rd and 4th Earls of Pembroke. He entered parliament in the interest of the Earls.
In 1624 Oldisworth became Member of Parliament for Old Sarum after Sir Arthur Ingram chose to sit for York instead. He was re-elected MP for Old Sarum in 1625, 1626 and 1628 and sat until 1629 when King Charles decided to rule without parliament for eleven years.
In April 1640, Oldisworth was elected MP for Salisbury in the Short Parliament. In November 1640 he was returned as MP for Salisbury and Plympton Erle and chose to sit for Salisbury. His patron was a puritan and had broken with the King, and Oldisworth continued to support the parliamentarian cause. He was appointed keeper of Windsor Great Park in 1650 and master of the prerogative office. He was satirised by royalist pamphleteers and praised by Herrick.
- W R Williams Parliamentary History of the County of Gloucester
- Willis, Browne (1750). Notitia Parliamentaria, Part II: A Series or Lists of the Representatives in the several Parliaments held from the Reformation 1541, to the Restoration 1660 ... London. pp. 229–239.
- William Thomas Lowndes, The bibliographer's manual of English literature, Volume 2
- Stephen B. Dobranski Readers and authorship in early modern England
- the Peerage.com
|Parliament of England|
Sir Robert Cotton, 1st Baronet, of Connington
Sir Arthur Ingram
|Member of Parliament for Old Sarum
With: Sir Robert Cotton, 1st Baronet, of Connington 1624
Sir Thomas Stradling 1625
Sir Benjamin Rudyerd 1626
Christopher Keightley 1628-1629
Parliament suspended until 1640
Parliament suspended since 1629
|Member of Parliament for Salisbury
With: Robert Hyde
Not represented in Barebones Parliament
Sir Nicholas Slanning
Sir Thomas Hele, 1st Baronet
|Member of Parliament for Plympton Erle
With: Sir Nicholas Slanning
Sir Richard Strode