6-K

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

REPORT OF FOREIGN PRIVATE ISSUER

Pursuant to Rule 13a-16 or 15d-16 of the

Securities Exchange Act of 1934

For the month of December 2025

Commission File Number: 001-41412

ioneer Ltd

(Translation of registrant’s name into English)

Suite 16.01, 213 Miller Street

North Sydney, NSW, 2060, Australia

(Address of principal executive offices)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.

Incorporation by Reference

The press release attached as Exhibit 99.1 hereto shall be deemed to be incorporated by reference into the registration statement on Form S-8 (File Number: 333-266137) of ioneer Ltd and to be a part thereof from the date on which this report is filed, to the extent not superseded by documents or reports subsequently filed or furnished.

EXHIBIT INDEX

The following exhibits are filed as part of this Form 6-K:

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

Exhibit 99.1

Appointment of Interim Chief Financial Officer

11 November 2025 – Ioneer Ltd (“Ioneer”) (ASX: INR, NASDAQ: IONR) is pleased to announce the appointment of April Hashimoto as its Interim Chief Financial Officer (CFO), effective 6 November 2025. April is based on the West Coast of North America in the same time zone as the Reno Office.

April brings extensive executive financial leadership experience, having most recently served in senior finance and CFO roles at Lithium Americas Corp and Pembrook Copper Corp respectively. She has deep international mining experience and has worked in both private and public companies. The Board is confident that she will provide strong financial stewardship during this transitional period.

This appointment follows the departure of Ian Bucknell, who will step down from the role effective 4 December 2025. The timing of April’s appointment allows for an orderly transition of the role.

The Company anticipates commencing a formal search process for a permanent CFO once the timing of a Final Investment Decision is known post the Strategic Partnering process and will update the market in due course.

Ioneer Managing Director Bernard Rowe said “I am pleased to welcome April to the ioneer executive team at this pivotal time for the company. April has extremely relevant recent experience in the lithium sector and is a highly skilled finance executive with a proven track record.”

This ASX release has been authorised by Ioneer Managing Director, Bernard Rowe.

--ENDS—

About Ioneer

Ioneer Ltd is an emerging lithium–boron producer and the 100% owner of the Rhyolite Ridge Lithium-Boron Project. Rhyolite Ridge is one of only a small number of lithium-boron ore deposits globally, and a linchpin project in Nevada’s burgeoning Lithium Loop.

Rhyolite Ridge closed a US$996 million loan with the U.S. Department of Energy Loan Programs Office under the Advanced Technology Vehicles Manufacturing program in January 2025. In October 2024, Ioneer received the final federal permit for the project from the Bureau of Land Management, concluding the formal federal permitting process which began in early 2020. Ioneer signed separate offtake agreements with Ford Motor Company and Prime Planet & Energy Solutions (joint venture between Toyota and Panasonic) in 2022 and Korea’s EcoPro Innovation in 2021.

To learn more about Ioneer, visit www.Ioneer.com/investors or join our online communities on X, Facebook, LinkedIn, Instagram and YouTube