What law prevents catholics from becoming the king or queen of england?
That should be the King or Queen of the United Kingdom as England stopped having a separate monarchy in 1603. The previous answers correctly refer to the Act of Settlement but it is perhaps helpful to understand why that Act was passed. Ever since the time of King Henry VIII there had been suspicion of catholics in England as it was felt to imply loyalty to the pope rather than to the king, especially as Henry required, as part of his breaking away from the catholic church, his top officials to swear an oath of loyalty to him as head of the English church. Famously, one of them, Sir Thomas More, refused and was executed for treason. In the 17th century, King Charles I was a catholic who tried to change the Church of England in a catholic direction, and also used his power in many ways that Parliament felt were an abuse of power. The result was the English Civil War, at the end of which Charles was tried for treason, found guilty and executed. Later in the century, his son King James II
