UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of

the Securities Exchange Act of 1934 (Amendment No.              )

Filed by the Registrant x

Filed by a Party other than the Registrant ¨

Check the appropriate box:

¨ Preliminary Proxy Statement

¨ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))

¨ Definitive Proxy Statement

x Definitive Additional Materials

¨ Soliciting Material under §240.14a-12

LIQUIDIA CORPORATION

(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

Payment of Filing Fee (Check the appropriate box):

x  No fee required.

¨ Fee computed on table below per Exchange Act Rules 14a-6(i)(1) and 0-11.

¨ Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-11.

Step 1: Go to www.envisionreports.com/LQDA. Step 2: Click on Cast Your Vote or Request Materials. Step 3: Follow the instructions on the screen to log in. www.envisionreports.com/LQDA Online Go to www.envisionreports.com/LQDA or scan the QR code — login details are located in the shaded bar below. Liquidia Corporation Stockholder Meeting Notice 03T7HC + + Important notice regarding the availability of proxy materials for the Liquidia Corporation 2023 Annual Stockholders Meeting to be held on June 15, 2023 Under Securities and Exchange Commission rules, you are receiving this notice that the proxy materials for the annual stockholders’ meeting are available on the Internet. Follow the instructions below to view the materials and vote online or request a copy. The items to be voted on and location of the annual meeting are on the reverse side. Your vote is important! This communication presents only an overview of the more complete proxy materials that are available to you on the Internet. We encourage you to access and review all of the important information contained in the proxy materials before voting. The 2023 proxy statement and 2023 annual report to Liquidia Corporation stockholders are available at: Obtaining a Copy of the Proxy Materials – If you want to receive a copy of the proxy materials, you must request one. There is no charge to you for requesting a copy. Please make your request as instructed on the reverse side on or before June 5, 2023 to facilitate timely delivery. 2NOT Easy Online Access — View your proxy materials and vote. When you go online, you can also help the environment by consenting to receive electronic delivery of future materials. Step 4: Make your selections as instructed on each screen for your delivery preferences. Step 5: Vote your shares. Votes submitted electronically must be received by June 14, 2023 at 11:59 P.M., local time. MMMMMMMMMMMM MMMMMMMMM MR A SAMPLE DESIGNATION (IF ANY) ADD 1 ADD 2 ADD 3 ADD 4 ADD 5 ADD 6 ENDORSEMENT_LINE______________ SACKPACK_____________ 1234 5678 9012 345 C 1234567890 COY 000004 MMMMMMM

Here’s how to order a copy of the proxy materials and select delivery preferences: Current and future delivery requests can be submitted using the options below. If you request an email copy, you will receive an email with a link to the current meeting materials. PLEASE NOTE: You must use the number in the shaded bar on the reverse side when requesting a copy of the proxy materials. — Internet – Go to www.envisionreports.com/LQDA. Click Cast Your Vote or Request Materials. — Phone – Call us free of charge at 1-866-641-4276. — Email – Send an email to investorvote@computershare.com with “Proxy Materials - Liquidia” in the subject line. Include your full name and address, plus the number located in the shaded bar on the reverse side, and state that you want a paper copy of the meeting materials. To facilitate timely delivery, all requests for a paper copy of proxy materials must be received by June 5, 2023. The Liquidia Corporation Annual Meeting of Stockholders will be held virtually on Thursday, June 15, 2023 at 4:30 p.m. local time at 419 Davis Drive, Suite 100, Morrisville, North Carolina 27560 and can be attended by visiting meetnow.global/MTWCDFM. Proposals to be voted on at the meeting are listed below along with the Board of Directors’ recommendations. The Board of Directors recommend a vote FOR all the nominees listed and FOR Proposals 2 and 3: 1. Election of Class II Directors: 01 – Katherine Rielly-Gauvin 02 – Raman Singh 03 – David Johnson 2. To approve an amendment to our Certificate of Incorporation to increase the number of authorized shares of our common stock from 80,000,000 shares to 100,000,000 shares. 3. To ratify the Appointment of PricewaterhouseCoopers LLP as the Company’s Independent Registered Public Accounting Firm for the Year Ending December 31, 2023. PLEASE NOTE – YOU CANNOT VOTE BY RETURNING THIS NOTICE. To vote your shares you must go online or request a paper copy of the proxy materials to receive a proxy card. Liquidia Corporation Stockholder Meeting Notice