Oswald Tesimond (1563 – 23 August 1636) was a Jesuit born in either Northumberland or York who, while not a direct conspirator, had some involvement in the Gunpowder Plot.
He was educated in York, in the Royal School of William and Mary in the Horse Fayre, which cost no money to attend. Guy Fawkes. Edward Oldcorne and brothers Christopher and John Wright were among Tesimond's classmates, all of whom would become involved in the Gunpowder Plot. Tesimond was entered into the Society of Jesus in 1584, but not before he left the English College in Rome, into which he had been first initiated; to leave the College and come into the Society, he required special permission from the cardinal protector (who was Giovanni Morone, at the time), which he successfully obtained.
Later, among other things, Tesimond studied theology in Messina, where he afterwards taught philosophy. In November 1587, some time before he left on a mission to England, he was ordained, but the exact date is unknown. As part of this mission, he arrived at Gravesend on 9 March 1598. For eight years he then worked with Edward Oldcorne in Worcestershire and Warwickshire before he was professed of the Jesuits' four vows on 28 October 1603.
He would later become somewhat involved in the Gunpowder Plot (see below). He effectively documented his experiences in a narrative which he wrote sometime after. He lived the later part of his life in various places, including Saint-Omer and Naples, where he died on 23 August 1636 at age 73.