The name "Act of Supremacy" is given to two separate acts of the English Parliament, one passed in 1534 and the other in 1559. Both acts had the same purpose; to firmly establish the English monarch as the official head of the Church of England, supplanting the power of the Catholic pope in Rome.

1534 Act of Supremacy
Henry's actions in assuming for himself the mantle of ecclesiastical authority were tinged with self-interest. He had sought in vain for papal approval for his divorce from Katherine of Aragon, and when it became clear that approval would not be forthcoming, Henry took matters into his own hands.

The Act of Supremacy must be seen as part of a broader policy, though, one aimed at increasing the power of the English monarch and decreasing the influence of Rome. To give him his due, Henry was probably sincere in his belief that the Church of England was riddled with poor administration and had long since lost the right to act as an independent body. (See our article on the Dissolution of the Monasteries).

At the same time, however, Henry had his eye on the wealth of the church, particularly the property of the monasteries. His lifestyle, and his desire for military glory had left Henry in a precarious financial position; he needed money, the church had lots of it, so the solution was obvious - take control of the church and its assets. This he did by asserting his legal right to act as head of the Church of England.

One important point to note is that the Act effectively made it treasonable to support the authority of the Pope over the Church of England. By tying the church and monarch so closely together, support for Catholicism became not simply a statement of personal religious conviction, but a repudiation of the authority of the monarch, and as such, an act of treason punishable by death.

Original text of Henry VIII's Act of Supremacy

1559 Act of Supremacy
Not surprisingly, Henry VIII's Act of Supremacy was repealed (1554) in the reign of his staunchly Catholic daughter, Mary I. Equally unsurprisingly, it was reinstated by Mary's Protestant sister, Elizabeth I, when she ascended the throne. Elizabeth declared herself Supreme Governor of the Church of England, and instituted an Oath of Supremacy, requiring anyone taking public or church office to swear allegiance to the monarch as head of the Church and state. Anyone refusing to take the Oath could be charged with treason.

There were three levels of penalties for refusal to take the Oath of Supremacy. A first refusal to resulted in loss of all movable goods. A second offence could mean life in prison and a loss of all real estate Possessions. A third offence would result in a charge of High Treason and death. A few years later the Oath was extended to include M.P.s and anyone taking a university degree.

Original text of Elizabeth I's Act of Supremacy

Related:
Dissolution of the Monasteries