T he Self-Denying Ordinance was a bill passed by the House of Commons on 19 December 1644 stipulating that no member of the House of Commons or the House of Lords could hold any command in the army or navy. Since this meant that nobles were automatically debarred from military command, the House of Lords threw it out in Janurary 1645. A second version of the bill was proposed under which all persons concerned were to resign, but without prejudice to their re-appointment. This was passed by both Houses on 3 April 1645.
The Ordinance was engineered by Sir Henry Vane and the Parliamentary "War Party" to rid Parliament's armies of its aristocratic commanders — some of whom were reluctant to inflict a decisive military defeat on the King and were leaning towards the Presbyterian "Peace Party" position of seeking a negotiated settlement. The Earls of Essex and Manchester lost their commands in the army and the Earl of Warwick lost control of the navy. The Presbyterian Sir William Waller resigned from the army rather than lose his political influence, as did the Independent Sir Arthur Haselrig. Oliver Cromwell remained exempt from the order since his military skills were regarded as indispensable. Sir WIlliam Brereton, engaged in directing the long drawn out siege of Chester, also retained his military command as well as his seat in Parliament.
The Ordinance prepared the way for the formation of the New Model Army