Mirum Pharmaceuticals Announces Closing of Public Offering and Full Exercise of Underwriters' Option to Purchase Additional Shares in Public Offering of Common Stock

Mirum Pharmaceuticals, Inc. (Nasdaq: MIRM), a biopharmaceutical company focused on the identification, acquisition, development and commercialization of novel therapies for debilitating rare and orphan diseases, today announced the closing of its previously announced underwritten public offering of 4,000,000 shares of its common stock, including the exercise in full by the underwriters of their option to purchase an additional 521,739 shares, at a price to the public of $23.00 per share. The gross proceeds to Mirum from the offering, before deducting underwriting discounts and commissions and offering expenses, were $92.0 million.

J.P. Morgan, SVB Securities and Evercore ISI acted as joint book-running managers for the offering. Raymond James acted as lead manager for the offering.

The offering was made pursuant to a shelf registration statement on Form S-3, including a base prospectus, that was previously filed with the Securities and Exchange Commission (the "SEC") and was declared effective by the SEC on August 12, 2020. A preliminary prospectus supplement and accompanying prospectus relating to the offering were filed with the SEC and are available for free on the SEC's website located at http://www.sec.gov. A final prospectus supplement and accompanying prospectus relating to the offering were filed with the SEC and are available for free on the SEC's website located at http://www.sec.gov. Copies of the final prospectus supplement and the accompanying prospectus relating to the offering may be obtained from:

J.P. Morgan Securities LLC, Attention: Broadridge Financial Solutions, 1155 Long Island Avenue, Edgewood, NY 11717, by email at [email protected] or by phone at (866) 803-9204; SVB Securities LLC, Attention: Syndicate Department, 53 State Street, 40th Floor, Boston, MA 02109, by email at [email protected] or by phone at (800) 808-7525, ext. 6105; or Evercore Group L.L.C., Attention: Equity Capital Markets, 55 East 52nd Street, New York, NY 10055, by email at [email protected] or by phone at (888) 474-0200.

This press release shall not constitute an offer to sell or a solicitation of an offer to buy, nor shall there be any sale of, these securities in any state or jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state or jurisdiction.

About Mirum Pharmaceuticals, Inc.

Mirum Pharmaceuticals, Inc. is a biopharmaceutical company dedicated to transforming the treatment of rare liver diseases. Mirum's approved medication is LIVMARLI® (maralixibat) oral solution which is approved in the U.S. for the treatment of cholestatic pruritus in patients with Alagille syndrome one year of age and older.

Mirum's late-stage pipeline includes two investigational treatments for debilitating liver diseases affecting children and adults. LIVMARLI, an oral ileal bile acid transporter (IBAT) inhibitor, is currently being evaluated in clinical trials for pediatric liver diseases and includes the MARCH Phase 3 clinical trial for progressive familial intrahepatic cholestasis (PFIC) and the EMBARK Phase 2b clinical trial for patients with biliary atresia. In addition, Mirum has an expanded access program open across multiple countries for eligible patients with ALGS and PFIC.

Mirum has submitted a Marketing Authorization Application to the European Medicines Agency for LIVMARLI for the treatment of cholestasis in patients with Alagille syndrome.

Mirum's second investigational treatment, volixibat, an oral IBAT inhibitor, is being evaluated in three potentially registrational studies including the VISTAS Phase 2b clinical trial for adults with primary sclerosing cholangitis, the OHANA Phase 2b clinical trial for pregnant women with intrahepatic cholestasis of pregnancy, and the VANTAGE Phase 2b clinical trial for adults with primary biliary cholangitis.