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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K

Commission file number: 1-7933

Aon plc

(Exact name of registrant as specified in its charter)

122 LEADENHALL STREET**,** LONDON**, ENGLAND** EC3V 4AN

(Address of principal executive offices) (Zip Code)

+44 20 7623 5500

(Registrant’s Telephone Number, Including Area Code) Securities registered pursuant to Section 12(b) of the Act:

S****ecurities registered pursuant to Section 12(g) of the Act: NONE

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes ☒ No ☐

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Exchange Act. Yes ☐ No ☒

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes ☒ No ☐

Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files). Yes ☒ No ☐

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K. ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

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. ☐

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yes ☐ No ☒

As of June 28, 2019, the aggregate market value of the registrant’s Class A Ordinary Shares held by non-affiliates of the registrant was $45,489,377,212 based on the closing sales price as reported on the New York Stock Exchange — Composite Transaction Listing.

Number of Class A Ordinary Shares of Aon plc, $0.01 nominal value, outstanding as of February 13, 2020: 231,582,094.

DOCUMENTS INCORPORATED BY REFERENCE

Aon plc has announced a transaction that, if completed, would result in an Irish public limited company becoming a successor issuer to Aon plc for purposes of Rule 12g-3 under the Securities Exchange Act of 1934, as amended. The proxy statement for the 2020 annual general meeting of shareholders of Aon plc, or if the transaction is completed, of such successor issuer, which meetings are in either case scheduled to be held on June 19, 2020, are incorporated by reference in this report in response to Part III, Items 10, 11, 12, 13 and 14.

Table of Contents

PART I