Well there are several very good reasons for this.

Firstly, Henry was a man of deep Christian Faith. He didn’t just believe, he thought long and hard about his faith. He earned the title Fidei Defensor from Pope Leo not just because he was a king but because his 30,000 word theological attack upon Protestantism (Assertio Septem Sacramentorum) was an utter best seller going through twenty editions in his lifetime.

This was why while he was able to break with Rome politically, Henry’s newly formed Church of England was fundamentally Catholic in terms of doctrine (although he veered between evangelical and conservative factions thereafter).

Given this, it would seem inconceivable that a man in such a high profile position, also one of deep faith, would justify the murder of someone; let alone royalty (as she was); let alone a woman. Nothing in any of his private writings suggests he would have ever considered such an idea. Indeed, all evidence suggests that Henry retained a great fear of poisoning for most of his adult life.

Yes he executed thousands; but all were done legally via the courts (this is not to say they were right; only that they were legal).

I am not claiming he was not guilty of cruelty and caprice; he once threatened Katherine Parr with being burned as a heretic for the sin of disagreeing with him over matters of religion (although this was towards the end of his life when his ulcerated legs were driving him towards cruelty and brutality); but the idea of assassination was by all accounts an anathema to him.

Even the two wives he executed were killed for treason (aka adultery towards the king). The legal distinction is crucial.

Secondly, her sudden death would have weakened his position drastically. Murder of a reigning monarch had never worked out well for the Plantagenet kings and while he was a strong king, Henry couldn’t escape the legacy of his father’s usurpation of the throne, not his weakened position in having no male heir.

Catherine suddenly dying would have left him vulnerable to allegations of skullduggery and that undermines the entire legal system. While centuries had passed since Henry II it would not have been lost upon the king how the murder of Beckett had caused the most powerful English monarch to humiliate himself as contrition.

Finally there is the issue of her status; she was a Queen. One did not ‘murder’ a queen without attacking the very social order itself. This was a lesson hard learned by his daughter Elizabeth who saw the execution of Mary of Scotland become the casus belli for Spain to go to war with England.

Catherine wasn’t a nobody; she was aunt of the Holy Roman Emperor Charles V, arguably the most powerful man in Europe, who was part of the most powerful dynasty in Europe. She was Queen of England. It could be argued that had she died in mysterious circumstances, even if it wasn’t used as an excuse for war, it would have impacted upon the prestige of his reign dramatically.

Thus Henry takes the legal approach; he moved to annul the union. And arguably he could have done so fairly easily had political circumstances in Europe had been more stable.

But refusal to annul forced him to break with Rome; and this led to the later issues.

By all accounts Catherine was a good mother, and a dutiful Queen; she never betrayed him, never conspired against him, even in the face of dreadful humiliation.

Indeed the very issue of the use of poison in Tudor England has sparked some interesting debates. Death by poison was considered to be a very foreign type of crime (compared to rape or burglary say) and cases were exceptionally rare.

There remained something subversive about the act- in principle it would allow the low-born murder the high; and this, coupled with his own fear of the act, was probably why Henry insisted on making murder by poison an act of High Treason, sentenced to death by boiling alive (a sentenced carried out on just two people; Richard Roos, the man convicted of the Fisher poisoning and a maid, Margret Davy in 1542.

Sources:

https://archive.is/A66gt At the bottom of this page is the actual law against poisoning Henry pushes through parliament. It describes the fate of those who resort so such deeds in marvellous gory detail.

Hutchinson, Robert; ‘The Last Days of Henry VIII’, 2005; Weidenfeld & Nicolson.

Hey there,

Just to let you know, your question is fine, and we're letting it stand. However, you should be aware that questions framed as 'Why didn't X do Y' relatively often don't get an answer that meets our standards (in our experience as moderators). There are a few reasons for this. Firstly, it often can be difficult to prove the counterfactual: historians know much more about what happened than what might have happened. Secondly, 'why didn't X do Y' questions are sometimes phrased in an ahistorical way. It's worth remembering that people in the past couldn't see into the future, and they generally didn't have all the information we now have about their situations; things that look obvious now didn't necessarily look that way at the time.

If you end up not getting a response after a day or two, consider asking a new question focusing instead on why what happened did happen (rather than why what didn't happen didn't happen) - this kind of question is more likely to get a response in our experience. Hope this helps!