Parliamentary approval for royal marriages

The Commonwealth Realms

I have no idea how common this is in general, but there is a law about it in the 16 Commonwealth Realms subject to the Perth Agreement 2011, that had Queen Elizabeth as their Sovereign at the time.

Before the agreement, the Royal Marriages Act 1772 was the relevant law in the UK and, through the doctrine of received law, applied in the former colonies. This rendered any Royal marriage entered into without the Sovereign's approval null and void. So, this is different from the Netherlands: it doesn't exclude these people from the line of succession because the marriage is a nullity - it never happened.

This Act had two problems:

1. It applied to anyone in the line of succession descended from George II (with some provisions about descendants of Princesses that meant that it might not actually apply to anyone). That's a lot of people, many of whom wouldn't even know they're subject to the Act.
2. The decision was not a Royal Prerogative, but rather a decision in Council: one made on the advice of the Ministers of the Government of the day (so, technically not Parliament). On whose Minister's advice was the decision to be taken - the UK? Australia? Canada? Saint Kitts and Nevis?

The Perth Agreement was the solution to this.

1. Only the first six people in the line of succession need permission to marry, and
2. The decision was to be made by the Sovereign in Council with respect to the United Kingdom, that is, the Government of the UK would grant or withhold consent.

Some other things the Perth Agreement did were to:

• retroactively legitimise any marriages that had breached the previous law,
• remove male-preferential primogeniture,i.e the first in line inherits irrespective of gender, and
• remove the disqualification from the line of succession for marrying a Roman Catholic, because sectarianism is no longer cool.

Netherlands

The situation in the Netherlands is somewhat different from the Commonwealth Realms. The Netherlands distinguishes between membership of the Royal Family, and membership of the Royal House. The membership of the House is defined by the constitution, and it is a subset of the Family. The current members are:

• King Willem-Alexander, his wife, and their three children, none of who are married as yet.
• Princess Beatrix, formerly Queen Beatrix, the King's mother.
• The King's youngest brother, and his wife.
• Princess Margriet, sister of Queen Beatrix, by an exception when the relevant law was last revised, and her husband.

The Netherlands Parliament has to approve marriages of members of the Royal House. If it does not approve them, the relevant person ceases to be a member of the House, but remains a member of the Family.

Prince Friso, the second son of Beatrix, married Mabel in 2004. Because she had not been entirely truthful about her previous associations with a known drug lord, the Netherlands government did not seek Parliamentary approval for the marriage, causing Prince Friso to lose his membership of the Royal House. He would have lost it anyway when Willem-Alexander succeeded to the throne, which happened in 2013. As it happened, he was brain-damaged by suffocation after being buried by an avalanche while skiing in 2012 and died a few months after his brother's succession.

Two other princes, sons of Princess Margriet, did not seek Parliamentary approval for their marriages in 2005, presumably because they would lose their membership of the Royal House anyway when Willem-Alexander succeeded.

A good democracy has various checks and balances between its political institutes to prevent the abuse of political power. In democracies that are also a Constitutional Monarchy, the Office of the Monarch is one of the political institutes that retains some political power. To ensure that a ruling Monarch doesn't abuse this power, some constitutions require a Monarch to consult the Legislature and / or the Executive. Marriage is often one such domain.

This is because historically, a royal could only marry another royalty and marriages to commoners was prohibited to them (unless they gave up their royal title). As royal suitors were often limited, and you don't want too much inbreeding in your Monarchical line, this meant that suitors often had to be considered from foreign royalty too.

Such kind of royal marriages, between royal families in different countries, were often also seen as an opportunity to create political alliances between 2 countries and / or also to improve diplomatic relations. Thus, it was often necessary for the government and the Parliament to get directly involved in the diplomatic negotiations of the marriage, which was essentially also very political in nature.

Another historic reason for getting the permission of the Legislature or the Executive for a Royal Marriage, has to do with the local politics itself. The Office of the Monarch being a political institute, the Monarch and their spouse, and their actions, all have a lot of political symbolism associated with it. Thus, for political stability, it was considered important to show that the government and the Monarch weren't in opposition on any major political issues. For example, when slavery of the coloured people was common, a Monarch marrying a person of colour would send very confusing messages to the public (as one of the reason often cited for slavery was that the white man was superior to a person of colour), and some politicians would consider it a political affront to their beliefs. This is also why royalties couldn't marry divorcees, as divorced men and women were considered lower in standing, and conservatives governments politically endorsed such ideas.