[1] Myddelton was born in Mincing Lane, London, but spent much of his adult life at Chirk, which his father gave him as a wedding present; he appears to have regarded himself as Welsh despite probably being unable to speak the language.

[1] A legal dispute with a neighbouring landowner at Chirk may have been what prompted him in 1624 to seek election to the 4th Parliament of King James I, initially as MP for Weymouth and Melcombe Regis, probably through the sponsorship of London merchant Robert Bateman.

His main concern appears to have been to find common ground with his fellow Puritan MPs, a term encompassing those who wanted to reform or "purify" the Anglican church, in order to present a united front against Catholic influence on the country.

[4] He was appointed Sergeant-Major General for North Wales in June 1643; despite lacking any previous military experience, he proved a reasonably competent field commander and was respected for "fair treatment" by his men.

[6] During the Second English Civil War he was again given overall responsibility for North Wales, where a short-lived rebellion under Sir John Owen was suppressed at Y Dalar Hir in June 1648, but left command in the field to Mytton.

[7] Although Royalist conspirators unsuccessfully attempted to draw him into a 1655 plot, he spent much of the 1650s at Chirk developing his commercial interests in coalmining, limiting his public life to attending the occasional horse race or cockfight.

[8] Welcoming a detachment of rebel cavalry to Chirk, he sent a trumpeter to invite the Oswestry militia to join them: they refused, but Myddelton instead led a group to Wrexham where on 7 August he drew his sword in the marketplace and declared Charles II as king.

[10] The government ordered a force under John Lambert to suppress the rebels, and after Booth's defeat at Winnington Bridge on 19 August, where Myddelton was probably present, the insurgency collapsed.

[6] His will contained an elaborate statement of his religious beliefs that nevertheless remained "politically evasive": "I am a Protestant, maintaining and believing the three Creeds established and professed by the Church of England in the time of Queen Elizabeth of blessed memory".