8-K

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

Date of Report (Date of earliest event reported)

May 6, 2020

Janus Henderson Group plc

(Exact name of registrant as specified in its charter)

201 Bishopsgate

EC2M 3AE

United Kingdom

(Address of principal executive offices) (Zip Code)

Registrant’s telephone number, including area code

+44 (0) 20 7818 1818

Not Applicable

(Former name or former address if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

Securities registered pursuant to Section 12(b)of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company o

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. o

On May 6, 2020, Janus Henderson Group plc (the “Company”) issued a press release announcing that the Company has amended the record date and payment date of its recently declared quarterly cash dividend of US$0.36 per share. The record date has been changed to May 18, 2020, from the previously announced date of May 11, 2020, and the payment date has been changed to June 3, 2020, from the previously announced date of May 27, 2020. This change ensures that the dividend record date is consistent with the New York Stock Exchange requirements.

(d)  Exhibits. The following exhibits are being furnished herewith.

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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 hereunto duly authorized.

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Exhibits 99.1

Janus Henderson Issues Amended DividendDates

LONDON — 6 May 2020 — Janus Henderson Group plc (NYSE/ASX: JHG) has amended the record date and payment date of its recently declared quarterly cash dividend of US$0.36 per share. The record date has been changed to 18 May 2020 from the previously announced date of 11 May 2020, and the payment date has been changed to 3 June 2020 from the previously announced date of 27 May 2020. This change assures that the dividend record date is consistent with the New York Stock Exchange requirements.

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About Janus Henderson

Janus Henderson Group is a leading global active asset manager dedicated to helping investors achieve long-term financial goals through a broad range of investment solutions, including equities, fixed income, quantitative equities, multi-asset and alternative asset class strategies.

At 31 March 2020, Janus Henderson had approximately US$294 billion in assets under management, more than 2,000 employees, and offices in 28 cities worldwide. Headquartered in London, the company is listed on the New York Stock Exchange (NYSE) and the Australian Securities Exchange (ASX).

Janus Henderson Group plc

47 Esplanade,

Jersey JE1 0BD

Registered in Jersey

No. 101484

ABN 67 133 992 766