Williams, 34, will join the Titans at the completion of the World Rugby Sevens Series next month as the NRLW's 10 franchises continue assembling their 24-player rosters ahead of the May 24 deadline.
Williams was a member of the Black Ferns side that collected silver in rugby sevens at the 2016 Rio Olympics and followed up with gold at the 2018 Commonwealth Games on the Gold Coast.
A neck injury ruled her out of the Tokyo Olympics, but she was part of New Zealand's bronze-medal side at last year's Commonwealth Games in Brisbane.
In rugby sevens, the versatile Williams plays either in the forwards or the backline. She has also captained New Zealand in touch football.
Williams' brother Sonny Bill became a household name during his premiership-winning NRL career with Canterbury before switching to rugby union and realising his All Blacks dream.
Titans coach Karyn Murphy said Niall Williams was intent on forging her own legacy in rugby league.
"Niall might have a famous surname but she is a very talented athlete in her own right with nearly 20 years of representative experience," Murphy said.
"Niall will bring an incredible amount of experience and professionalism to our squad, and her extreme athletic ability, speed and agility is why she is a very versatile player that will make a valuable contribution to our team."
The Titans endured a tough first season under Murphy in 2022, managing only one win and finishing bottom of the ladder.
Gold Coast will hope Williams' leadership can help them turn the tide when the new season begins in July.
"In extension to her playing ability, her values, passion and energy for the community aligns hand-in-hand with our club's purpose and I'm so excited for Niall to reach new heights on and off the field with us here at the Titans," Murphy said.
Shaylee Bent, Taliah Fuimaono and Kaitlyn Phillips are among the other players joining Gold Coast for their third NRLW campaign.
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