Centuries-old royal succession laws are one step closer to modernization after the heads of Commonwealth countries agreed on Friday to remove gender-discrimination from the process used to choose the next monarch.

Under the 1701 Act of Settlement, a male heir takes precedence over female siblings and would leapfrog any older sisters to the throne.

Due largely in part to the enormous popularity of Prince William and his wife the Duchess of Cambridge, there has been a concerted push to update the laws to ensure the couple's firstborn will be the heir, regardless of gender.

The heads of all 16 Commonwealth countries still under the Queen must agree unanimously to any changes to the Act of Settlement, in order to ensure all members recognize the same monarch.

On Friday, they did just that, agreeing to the proposed changes.

"Put simply, if the Duke and Duchess of Cambridge were to have a little girl, that girl would one day be our queen," said British Prime Minister David Cameron in announcing the changes.

The leaders also agreed to remove a rule that banned the king or queen from marrying a Catholic.

Prime Minister Stephen Harper called the updates "obvious modernizations" that are long overdue.

"There was universal agreement, unanimous agreement that these changes simply recognize the equality of women and Catholics and they're long overdue," Harper said.

While the Commonwealth leaders have agreed to the changes, they will still have to be approved by their governments. Harper gave no timeline for when the House of Commons will vote on the amendment.

Cameron wrote to all the Commonwealth leaders ahead of the summit, outlining his plan for reform and asking for their support.

Cameron said the antiquated laws simply don't fit with the values that the Commonwealth holds dear.

"We espouse gender equality in all other aspects of life and it is an anomaly that in the rules relating to the highest public office we continue to enshrine male superiority," Cameron wrote in his letter.

CTV's Richard Madan, travelling with Harper, said the 54 leaders taking part in the summit in Perth are also looking at updating human rights protections within the Commonwealth.

He said a working group has suggested the appointment of a commissioner of human rights to ensure standards are maintained across the Commonwealth. Madan said accusations of human rights abuses in Commonwealth countries are often not investigated.

"Of the 54 member states in the Commonwealth there's criticism that 40 of those countries still consider homosexuality a criminal offence, so there's a push to change that," Madan told CTV's Canada AM.