QuickLinks -- Click here to rapidly navigate through this document

FORM 6-K

SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549

~~Washington,~~Report ~~D.C.~~of ~~20549~~Foreign Private Issuer

~~Report~~ ~~of Foreign Private Issuer~~ Pursuant to Rule 13a-16 or 15d-16 of ~~the Securities Exchange Act of 1934~~

~~For~~ the ~~month~~Securities Exchange Act of ~~October 2004~~1934

~~Commission~~For ~~File~~the ~~Number 000-30716~~month of January 2005

AUTONOMY CORPORATION PLC

Commission File Number 000-30716

Cambridge Business Park
Cowley Road
Cambridge CB4 0WZ
United Kingdom
Tel: 44 (0)1223 448 000
(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.

Form 20-F ~~[X]~~ ý Form 40-F o ~~[ ]~~

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1): ~~____~~

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T ~~Rule~~ Rule 101(b)(7): ~~____~~

Indicate by check mark whether the registrant by furnishing the information contained in this Form is also thereby furnishing the information to the Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934.

Yes [ ] o No ~~[X]~~ ý

If "Yes" is marked, indicate below the file number assigned to the registrant in connection with Rule 12g3-2(b): 82-~~_____~~ .

On ~~October~~each of 1 December 2004, 2 December 2004, 3 December 2004, 8 December 2004, 10 December 2004, 2013 December 2004, 14 December 2004, ~~Autonomy~~15 December 2004, ~~Corporation~~16 December 2004, ~~plc~~17 December 2004 ~~(the~~and "20 December 2004 the Company") issued a ~~press~~ release ~~announcing~~through the ~~Company~~London Stock Exchange's ~~results~~Registered ~~for~~News Service in accordance with the ~~three~~Listing ~~and~~Rules ~~nine~~of ~~months~~the ~~ended September~~United ~~30,~~Kingdom ~~2004.~~Listing AAuthority, ~~copy~~announcing details of purchases by the ~~press~~Company ~~release~~of isits own shares for cancellation. Copies of the releases are attached hereto as Exhibit 99.1 and are incorporated herein by reference.

~~Exhibits~~ On 31 December 2004 the Company issued a release announcing that the Company was to voluntarily terminate its American Depositary Receipt program. A copy of the release is attached hereto as Exhibit 99.2 and is incorporated herein by reference.

99.1 Press Release issued on October 20, 2004, announcing results for the three and nine months ended September 30, 2004.

Exhibits
99.1		Releases issued on each of 1 December 2004, 2 December 2004, 3 December 2004, 8 December 2004, 10 December 2004, 13 December 2004, 14 December 2004, 15 December 2004, 16 December 2004, 17 December 2004 and 20 December 2004 announcing details of purchases by the Company of its own shares for cancellation.
99.2		Release issued on 31 December 2004 that the Company was to voluntarily terminate its American Depositary Receipt program.

SIGNATURES

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.

AUTONOMY CORPORATION PLC

	AUTONOMY CORPORATION PLC

Date: 5 January 2005	By:	/s/ ANDREW M. KANTER Andrew M. Kanter Chief Operating Officer

~~Date:~~ ~~October 21,~~ ~~2004 By: /s/~~AUTONOMY ~~Andrew~~CORPORATION M.PLC INDEX ~~Kanter Andrew~~TO ~~M. Kanter~~ EXHIBITS ~~Chief Operating Officer~~

AUTONOMY CORPORATION PLC

Exhibit Number		Description
99.1		Releases issued on each of 1 December 2004, 2 December 2004, 3 December 2004, 8 December 2004, 10 December 2004, 13 December 2004, 14 December 2004, 15 December 2004, 16 December 2004, 17 December 2004 and 20 December 2004 announcing details of purchases by the Company of its own shares for cancellation.
99.2		Release issued on 31 December 2004 that the Company was to voluntarily terminate its American Depositary Receipt program.

~~INDEX TO EXHIBITS~~QuickLinks

SIGNATURES
INDEX TO EXHIBITS

Exhibit Number Description 99.1 Press Release issued on October 20, 2004, announcing results for the three and nine months ended September 30, 2004.

Filing Compare · AUTONOMY CORP PLC