Sir Nathaniel Catelyn (c. 1580 – 1637) (whose family name is also spelt Catlyn or Catlin), was a leading English-born politician and judge in seventeenth-century Ireland. He was Speaker of the Irish House of Commons in the Irish Parliament of 1634–5, Recorder of Dublin and the first holder of the office of Second Serjeant. Despite accusations of conflict of interest and of Roman Catholic sympathies, he retained the confidence of the Crown and was a key ally of Thomas Wentworth, 1st Earl of Strafford, the Lord Deputy of Ireland.