Family and life before 1605
Born in about 1567, Francis Tresham was the eldest son of Sir Thomas Tresham, of Rushton Hall in Northamptonshire, and Meriel Throckmorton, daughter of Sir Robert Throckmorton of Coughton in Warwickshire and his wife Elizabeth Hussey. According to the antiquary Anthony Wood, Tresham was educated in Oxford at either St John's College or Gloucester Hall or both, although biographer Mark Nicholls mentions that there appears to be no other evidence to corroborate that claim.
Francis is said to have been a fellow prisoner with Robert Catesby held in Wisbech Castle at the time of the Spanish Armada.
He married Anne Tufton, daughter of Sir John Tufton of Hothfield in Kent, in 1593. The couple had three children, twins Lucy and Thomas (b.1598), and Elizabeth. Thomas died in infancy, Lucy became a nun in Brussels, and Elizabeth married Sir George Heneage of Hainton, Lincolnshire.
Tresham's father, born near the end of Henry VIII's reign, was regarded by the Catholic community as one of its leaders. Thomas was received into the Catholic Church in 1580, and in the same year he allowed the Jesuit Edmund Campion to stay at his house in Hoxton. For the latter, following Campion's capture in 1581, he was tried in Star Chamber. Thomas's refusal to fully comply with his interrogators was the beginning of years of fines and spells in prison. He proclaimed the accession of James I to the English throne, but the king's promises to Thomas of forestry commissions and an end to recusancy fines were not kept. His finances were seriously depleted by fines of £7,720 for recusancy, and the spending of £12,200 on the marriages of six daughters meant that when he died in 1605, his estate was £11,500 in debt.
Author Antonia Fraser suggests that as a young man Francis became "resentful of his father's authority and profligate with his father's money." Authors Peter Marshall and Geoffrey Scott describe him as possessing a "somewhat hot-headed nature", while another source calls him a "wild unstayed man". The Jesuit priest Oswald Tesimond wrote that he was "a man of sound judgement. He knew how to look after himself, but was not much to be trusted". While still young he assaulted a man and his pregnant daughter, claiming that their family owed his father money. Tresham spent time in prison for this offence.
On 8 February 1601 he joined the Earl of Essex in open rebellion against the government. Essex's aim was to secure his own ambitions, but the Jesuit Henry Garnet described the young men who accompanied him as being interested mostly in furthering the Catholic cause. Captured and imprisoned, Tresham appealed to Katherine Howard, Lady Howard de Walden, but was rebuked. His sister, Lady Monteagle, alerted his cousin John Throckmorton, who turned to "three most honorable parsons and one especiall instrument" for help. The identity of these individuals is unclear, but Tresham was promised freedom on the condition that over the next three months his father pay £2,100 to William Ayloffe, to "save his lyef attainder in bloode." He was released on 21 June. The experience did not dissuade him from engaging in further conspiracies; in 1602 and 1603 he was involved in the missions to Catholic Spain made by Thomas Wintour, Anthony Dutton (possibly an alias of Christopher Wright) and Guy Fawkes, later dubbed by the English government as the Spanish Treason. However, upon James's accession to the throne, he told Thomas Wintour (secretary to Tresham's brother-in-law William Parker, 4th Baron Monteagle), that he would "stand wholly for the King", and "to have no speech with him of Spain."
His father tried to have him appointed as keeper of the deer parks at Brigstock. This was resisted by the villagers in May 1603, who objected to the Tresham family's recusancy. One of Tresham's servants Thomas Walker was installed at a lodge in Brigstock and Catholics gathered at the lodge at night.