The rules of succession to the throne belong to a "bygone era", Deputy Prime Minister Nick Clegg said as MPs considered major changes to the constitution.
The legislation will end discrimination against future female royals so that men will no longer take precedence over women in the order of succession and also end the bar on heirs marrying Roman Catholics if they want to keep their entitlement to the throne.
The changes will mean the Duke and Duchess of Cambridge's first child, expected in July, can become monarch even if it is a girl who later has younger brothers.
As the Succession to the Crown Bill faced its second reading, Mr Clegg said: "The current rules of succession belong to a bygone era. They reflect old prejudices and old fears.
"Today we don't support laws which discriminate on either religious or gender grounds, they have no place in modern Britain and certainly not in our monarchy, an an institution central to our constitution, to the Commonwealth and to our national identity too."
The current rules were based on "supposed superiority of men", Mr Clegg said.
"That anachronism is out of step with out society. It sends the wrong message to the rest of the world and it's time for the rules to change."
The legislation also replaces the 1772 Royal Marriages Act which requires descendants of George II to seek the reigning monarch's consent before marrying, without which the union is void.
Mr Clegg said: "This law, passed 240 years ago, is clearly now unworkable. George II's descendants number in their hundreds, many will be unaware of this arcane requirement. Many will have only a tenuous link to the Royal Family.
"The Bill proposes that the monarch need only consent to the marriages of the first six individuals in the line of succession, without which they will lose their place."
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