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 UNDER

THE SECURITIES EXCHANGE ACT OF 1934

For the month of June 2025

Commission File Number: 001-38638

NIOInc.

(Registrant’s Name)

Building 19, No. 1355, Caobao Road, MinhangDistrict

Shanghai, People’s Republic of China

(Address of Principal Executive Offices)

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

Form 20-F x             Form 40-F ¨

EXPLANATORY NOTE

We, NIO Inc., hereby announce that our 2025 annual general meetingof shareholders (the “AGM”) was held in Shanghai on June 25, 2025, and the proposed resolution set out in thenotice of AGM was duly passed.

We made an announcement dated June 25, 2025 with The Stock Exchangeof Hong Kong Limited in relation to the poll results of the 2025 AGM. For details, please refer to exhibit 99.1 to this current reporton Form 6-K.

EXHIBIT INDEX

SIGNATURES

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

Date: June 25, 2025

Exhibit 99.1

Hong Kong Exchanges and Clearing Limitedand The Stock Exchange of Hong Kong Limited take no responsibility for the contents of this announcement, make no representation as toits accuracy or completeness and expressly disclaim any liability whatsoever for any loss howsoever arising from or in reliance upon thewhole or any part of the contents of this announcement.

Under our weighted voting rights structure,our share capital comprises Class A ordinary shares and Class C ordinary shares. Each Class A ordinary share entitles the holder to exerciseone vote, and each Class C ordinary share entitles the holder to exercise eight votes, respectively, on any resolution tabled at our generalmeetings, except as may otherwise be required by law or by the Rules Governing the Listing of Securities on The Stock Exchange of HongKong Limited or provided for in our memorandum and articles of association. Shareholders and prospective investors should be aware ofthe potential risks of investing in a company with a weighted voting rights structure. Our American depositary shares, each representingone of our Class A ordinary shares, are listed on the New York Stock Exchange in the United States under the symbol NIO.

NIOInc.

(A company controlledthrough weighted voting rights and
incorporated in the Cayman Islands with limited liability)

(Stock Code: 9866)

POLLRESULTS OF THE 2025 ANNUAL GENERAL MEETING

We wish to announce that the proposed resolution set out inour notice of the annual general meeting dated May 23, 2025 was duly passed at our annual general meeting held on June 25, 2025.

Hong Kong, June 25, 2025

As of the date of this announcement,the board of directors of the Company comprises Mr. Bin Li as the chairman, Mr. Lihong Qin as the director, Mr. Eddy Georges Skaf andMr. Nicholas Paul Collins as the non-executive directors, and Mr. Hai Wu, Mr. Denny Ting Bun Lee, Ms. Yu Long and Mr. Yonggang Wen asthe independent directors.