It's the fifth time since 2010 the names have both been the most popular. Oliver has been the number one name for boys every year since 2014.

Attorney General Mark Speakman said when it came to baby names, parents were sticking with centuries-old favourites.

"Despite Game of Thrones frenzy reaching fever pitch, names like Daenerys, Arya, Tyrion and even the once ubiquitous John are nowhere to be seen in the NSW Registry of Births Deaths & Marriages top 100 baby names for 2018," he said.

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Names favoured by royalty continue to chart highly, with William the second most popular boys' name and Harry jumping to 15. George, Edward, Louis and Charles also feature on the list.

Popular royal names for girls include Mia, Isla, Sophie, Zara, Elizabeth and Savannah.

"Huge crowds greeted Prince Harry and Meghan Markle when they visited NSW in October last year so it's no surprise royal names are in fashion," Mr Speakman said.

"The Duke and Duchess of Sussex are about to welcome their first child and no doubt many NSW parents will be looking to them for inspiration."