Francis Tresham was a member of the group of English provincial Catholics who planned the failed Gunpowder Plot of 1605, a conspiracy to assassinate King James I of England. Tresham was imprisoned for his part in the Earl of Essex's failed rebellion against the government in 1601, and only his family's intervention and his father's money saved him from being attainted. The incident did not stop him from becoming involved in two missions to Catholic Spain to seek support for English Catholics (then heavily persecuted) – and finally with the Gunpowder Plotters.
According to his confession, Tresham joined the plot in October of 1605. Its leader Robert Catesby asked him to provide a large sum of money and the use of Rushton Hall, but Tresham apparently provided neither, instead giving a much smaller amount of money to fellow plotter Thomas Wintour. Tresham also expressed his concern that two of his brothers-in-law would be killed if the plot succeeded. An anonymous letter delivered to one of them, William Parker, 4th Baron Monteagle, was handed over to Robert Cecil, 1st Earl of Salisbury, and eventually proved decisive in foiling the conspiracy.
Historians have long suspected that Tresham wrote the letter, a hypothesis that remains unproven. Catesby and Wintour also thought that Tresham was the letter's author and threatened to kill him, but he was able to convince them otherwise. Tresham was arrested on 12 November and confined in the Tower of London. In his confession he sought to allay his involvement in the plot, but never mentioned the letter. He died of natural causes on December 23rd, 1605.