Completion of Placing

THIS ANNOUNCEMENT AND THE INFORMATION CONTAINED HEREIN IS RESTRICTED AND, SUBJECT TO CERTAIN EXCEPTIONS, IS NOT FOR RELEASE, PUBLICATION OR DISTRIBUTION, IN WHOLE OR IN PART, DIRECTLY OR INDIRECTLY IN, OR INTO OR FROM THE UNITED STATES, AUSTRALIA, CANADA (EXCEPT IN COMPLIANCE WITH CANADIAN SECURITIES LAWS), JAPAN, NEW ZEALAND, THE REPUBLIC OF IRELAND OR THE REPUBLIC OF SOUTH AFRICA OR ANY OTHER JURISDICTION IN WHICH THE SAME WOULD BE UNLAWFUL.

FURTHER, THIS ANNOUNCEMENT IS FOR INFORMATION PURPOSES ONLY AND SHALL NOT CONSTITUTE AN OFFER TO SELL OR ISSUE OR THE SOLICITATION TO BUY, SUBSCRIBE FOR OR OTHERWISE ACQUIRE ANY ORDINARY SHARES OF HORIZON IN ANY JURISDICTION IN WHICH ANY SUCH OFFER OR SOLICITATION WOULD BE UNLAWFUL. THIS ANNOUNCEMENT SHOULD BE READ IN ITS ENTIRETY.

THE SECURITIES REFERRED TO HEREIN MAY NOT BE OFFERED OR SOLD IN THE UNITED STATES ABSENT REGISTRATION OR AN EXEMPTION FROM REGISTRATION UNDER THE U.S. SECURITIES ACT OF 1933, AS AMENDED. THE COMPANY DOES NOT INTEND TO REGISTER ANY OF THE SECURITIES IN THE UNITED STATES OR TO CONDUCT A PUBLIC OFFERING OF THE SECURITIES IN THE UNITED STATES.

Horizon Discovery Group plc ("Horizon" or the "Company")

Completion of Placing

Cambridge, UK, 23 August 2017: Horizon Discovery Group plc (LSE: HZD) ("Horizon" or "the Company"), a global leader in the application of gene editing technologies, is pleased to announce that, further to the announcements made by the Company on 19 July 2017 and 22 August 2017, 39,024,390 Placing Shares have this morning been admitted to trading on AIM, raising gross proceeds of £80 million for the Company. Following this, the Company expects completion of its acquisition of GE Healthcare Dharmacon, Inc. to occur on 31 August 2017.

Following the admission of the Placing Shares, the Company's enlarged issued share capital now comprises 135,851,082 Ordinary Shares with one voting right per share. No shares are held in Treasury. The total number of voting rights in the Company is therefore 135,851,082.

This figure of 135,851,082 Ordinary Shares may be used by shareholders as the denominator for the calculations by which they will determine if they are required to notify their interest in, or a change to their interest in, the share capital of the Company under the FCA's Disclosure and Transparency Rules.

Unless otherwise indicated, capitalised terms in this announcement have the same meaning as in the Acquisition announcement released by Horizon on 19 July 2017.

ENDS

For further information from Horizon Discovery Group plc, please contact:

Horizon Discovery Group plc

Darrin Disley, Chief Executive Officer

Richard Vellacott, Chief Financial Officer

Chris Claxton, VP Investor Relations

Tel: +44 (0) 1223 655 580

Numis Securities Limited (Broker and NOMAD)

Michael Meade / Freddie Barnfield

Tel: +44 (0) 207 260 1000

Consilium Strategic Communications (Financial Media and Investor Relations)

Mary-Jane Elliott / Susan Stuart / Matthew Neal / Melissa Gardiner

Tel: +44 (0) 20 3709 5701

Email: [email protected]

About Horizon Discovery Group plc ‐ see www.horizondiscovery.com

Horizon Discovery Group plc (LSE: HZD) ("Horizon"), is a leading global gene editing company that designs and engineers genetically-modified cells and then applies them in research and clinical applications that advance human health.

Horizon's core capabilities are built around its proprietary translational genomics platform, a highly precise and flexible suite of gene editing tools (rAAV, ZFN, CRISPR and Transposon) able to alter almost any gene sequence in human or mammalian cell-lines.

Horizon offers over 23,000 catalogue products and related research services based on the generation and application of cell and animal models that accurately recapitulate the disease-causing genetic anomalies found in diseases like cancer. Horizon's commercial offering has been adopted by over 1,600 unique research organisations in over 50 countries, as well as in the Company's own pipeline of innovation, to support a greater understanding of the genetic drivers of disease and the development of molecular, cell and gene therapies that can be prescribed on a personalised basis.

Horizon is headquartered in Cambridge, UK, and is listed on the London Stock Exchange's AIM market under the ticker "HZD".